Furr the entire ceiling down with strapping, attach the plates into the furring.

Casey

How would furring strips along the ceiling solve the problem? Then I'd have to add furring strips to the entire basement (2,200 square feet) to level out the ceiling all around.

Casey it right; strapping is the best way to level and attach a ceiling whatever the structure. Solid blocking would be necessary only for better sound separation. Splitting should not be an issue with strapping but you could pre-drill and use screws.

Hot melt the blocking in place. And yes, you're over thinking it.

If you need to pass inspection you will need mechanical fasteners. Panel reinforcing is commonly nailed to the sides of I-Joist flanges with 8d nails @ 6" o.c. but it might be wise to limit the size of toenailing to 10d. The brace is only acting horizontally so the nails won't need to resist much. If you are concerned about splitting, turn each nail over, hold it against a solid surface and tap it with a hammer.

This is for non-load bearing walls, so metal strapping seems to be overdoing it.

Regardless, I finally found some best-practices documentation from one of the major I-joist manufacturers... they show nailing through the flange as appropriate for blocking/strapping, so that's what I'm going with.

I'm the same. I prefer to not nail sideways through a flange due to the possibility of the flange delaminating. Here's what I've done in the past. Approved by the manufacturer:

Cut a length of 2x4 blocking long enough to go web-to-web across the joist bay. I run a bead of PL then install the blocking and nail it off. I fasten through the web and into the end grain of the blocking. Two fasteners per end.

For a 2x4 partition wall I'll then run a 2x6 in the direction of the partition wall, centered on the centerline of the future partition wall. With the 2x4 being the same thickness as the joist flanges, it'll act as a filler, and by it protruding an inch past each edge of the top plate of the soon to be installed partition wall, it'll act as a backer to support the floating edge of the ceiling drywall.

Where I live a builder would strap the ceiling whether you specified it or not in order to be able to add shims to level the ceiling. If you use the above detail, don't attach the edge of the ceiling board to the blocking.

I'm with you, Mongo.