even a well drawn sketch would help

You have this shower pan and want to build a wall on top of part of one of the long sides?

You don't have room to build the wall outside the pan?

If I'm understanding your post correctly...it depends on the construction/design of the pan.

If the pan can't bear the weight of the wall framed right on top of it, probably the easiest would be to build a 2x6 wall and notch out the bottom of one side of the studs to go over the curb.

Example...let's say your curb is 4" wide and 3" high. Think of the stud standing vertically. You'd want the notch to be tall enough to clear the curb height, say 3-1/8" to 3-1/4". You'd want the notch to be deep enough to cover most of the curb, but not so deep that the stud is too fragile after it is notched. So for this example make the notch 2-3/4" deep, leaving 2-3/4" of the 5-1/2" width of the 2x6 uncut. A 2-3/4" deep notch will cover 2-3/4" of the 4" of curb width, leaving 1-1/4" of the curb exposed.

In the drawing below, think of the "x" as the stud and the "o" as the pan. You can see how the stud is notched out to accept the pan. The "z" is the sole plate for the wall. You'll have two sole plates. One at the bottom of the wall that will sit on the bathroom floor, one at the bottom of the notch that will sit just above the top of the pan's curb. "c" is the cement board and "t" is the tile.

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When you add the cement board and tile to the inside face of the wall, it'll build it out a bit, but a bit of the edge of the curb will remain visible. How much depends on the style of the curb, if the edge is closer to square, or if it has a generous radius, etc. If you use 6-mil poly in that wall, seal the bottom edge of it to the top of the curb.

In this case, your curb is 4" thick, the notch is 2-3/4" deep, leaving 1-1/4" of curb exposed. The 1/2" of cement board, the 1/8" thickness of thinset, and the 1/4" thickness of the tile will cover another 7/8ths-inch of the curb, leaving 3/8" of the curb exposed.

One other comment...if the inside edge of the curb is dead straight then all will look fine. If the inside edge of the curb waivers in and out a bit, that 3/8" of curb might go from 3/8", to 1/2", to 1/4", etc, as the curb waffles around. The more your curb waffles in and out, the more curb you need to leave exposed to compensate for the waffling.

With 2x6 framing, this will be a "thick" wall. A great opportunity to use the stud bays for storage. A shower niche on the inside, or a tall "medicine cabinet" or "storage pantry" built in to the stud bays on the opposite side.

Thanks, all for the responses. To clarify, the problem is that the shower pan is designed to receive a full-panel glass door, but we didn't know that when we ordered it! We could do the shower door, but our true desire is to have a wall that comes about 2/3 across the front of the shower, and leaves the remaining 1/3 as a "door." We're hesitant to do this because we don't want the water to leak into the wall, obviously. I had thought about the notching, mongoct, and I do think that is the way to go. I don't want to build the wall directly on top of the shower curb, but a slight overlap (notch) may help to seal the joint as far as I'm concerned. I'm trying to figure out how to to flashing for that joint. 6 mil plastic might work just fine--thanks for the suggestion. Any other materials I should consider? What is a good sealer to use in this application? Bottom line is I don't want water coming out into that wall. Love the idea about 2x6s and building in shelving. What a great idea. I'm thinking we may be able to rig this wall after all. Any other thoughts are most welcome. Thanks to all who have read and thought about our problem!!