Shower Pan Blocking With Plumbing in the Way

I need advice on best way to do blocking for a shower pan when there is plumbing between the 2x4s in the wall where the blocking should go. In my case, there are 2 water copper supply lines coming up through the floor then running parallel to the floor and then back up, a 1-1/2" ABS vent, and some central vac lines. Some of this plumbing is within 1/2" of the front of the framing. So I can't just use 2X10s for blocking for the shower pan (unless I do some very fancy routeing).

Is it OK to just trim 1/2" off the 2" side of 2x4s (or use 2X2s), then use these to build around the plumbing (leaving 1/2" gap from front of framing), notching the lumber where necessary, and then nail 1/2" plywood to the face of the whole thing to block it all off? <hope this is clear>.

Any other ideas? Thanks much.

That should work. An alternative would be to use a surface membrane system rather than a conventional liner. You just need a surface to support the liner and the cbu. Remember to provide room in the corners for the folds of the liner.

Have you looked at Kerdi from www.schluter.com?
Personally, I think it works better and even if your floor requires a mud pan, you only need the one layer and the walls can be put up with drywall, including the curb. Having a waterproof layer immediately under the tile (whoever's system you choose) means the shower dries out much quicker and it contains moisture better.