Linda:

I would cover them deeply with compost, or stable manure. The fact that the root systems are shallow does not mean you cannot cover them. Keep doing it.

Don Yellman, Great Falls, VA

Use Southern Highbush varieties. They take drying out better. Set up a soaker hose/drip emitter system so that each day they get some water. Possibly use sawdust or shavings as a top dressing. (If you do this it is good to spray it with urea fertilizer) Just some suggestions.
Another thing is you might check with your ag university for suggestions they have.

Here is a link that might be useful: Clemson

...so the nature of your sand soil, Linda, is the loose dry type? ("sands" can vary so much, from very porous to quite waterlogged (or leaning that way) that recommendations could run almost in opposites depending upon the type of sand involved.
I think I have to agree with the basic overtones of the discussion here so far answers--that one way or another, some kind of mulching , as well as probably watering or irrigating in some very RELIABLE dependable way, look to be in the cards here.

At the same time, blueberry culture being as usual being apt to sometimes be a fairly tough call, especially as to soils, the situation (as you seem to realize, given how detailed you have made your "post" here) may be "other than" an easy, simple one!

Among various factors and considerations to be faced, is one
possibly overriding principle type one, which I think might best be taken to heart here and now as to remedial plans here: blueberries under permanent, heavy mulch, may be very apt to very much grow (roots) "up into" said mulch. To the point that the heavy mulch, gradually decomposing and regularly being supplemented/renewed to maintain or increase its depth, can fairly well "become" the essential (new) "soil" of the plants and thus, the "soil" that they come to basically be growing in. It's somewhat as though the original soil isn't even there. Which, under difficult original soil conditions, is not necessarily a bad thing-- may be what's in order and what the situation wants. "But"-- this new state of affairs, can be (most likely "will" be) permanent and irreversible.
In other words, it may be "fine" to go with deep mulching of blueberries and the Situation Taking-over By-the-Mulch that can be expected --but it might be best to realize up-front the permanent committment here: perennial maintaining/renewal of the mulch; likely permanent need for fertilizing adjustment (such as gmason suggests in his guidelines even for a related plan of just drip-irrigation/with-maybe-light-mulching).
Maybe supplemental watering/irrigating, especially for best prospects for acceptable flavor (more about this below).

For deep permanent mulch culture of blueberries, a deep layer of sawdust I understand is considered clearly the most effective, though various other materials, are likely to work all right provided they can be maintained deeply enough (most other materials seem to be less lasting and more often in need of replenishing, than sawdust or similar materials like wood chips.
One modest note of caution about blueberry growing in sawdust mulch culture ( I "suspect" --while am not completely certain-- this probably applies much less, if much at all, to oher types of mulches, except maybe somewhat to other very woody materials , for example wood chips, especially resinous "softwood" ones such as pine or similar), is that, during many years, there distinctly tend to be, under sawdust mulch, a certain degree of flavor problems, specifically tendency toward harshness and lack of sweetness. And while the harshness semi-bitterness aspect may be defeatable by letting picked berries age at room temperature for a day or two, this unfortunately doesn't seem to add any sweetness..
So overall as to this Discussion and Topic here, maybe all of this, would , hmnn, seem to point right to gmason's suggested plan of mainly aiming for irrigation and fertilizing and minor mulching to overcome the sandy soil problem.,,,The question there being that of the possibilites your specific sort of sand soil and site, and situation, offer or don't offer as to likelihood of being able "to get away with" this latter, less involved approach...

"It's lucky Blueberries are so great...Otherwise, putting up with them would be ???"