You can glue in the drain (make sure it's level) and then mud later. Just use a stick to pack the mud under the drain flange. The Kerdi drain comes with a couple of styrofoam blocks that you can use to space it up correctly (1 to 1.5" of the slab)

Pete: Thanks. I'm planning on the drain to be 1.25 inches off the slab...should be interesting. Another question. The bathroom had walll paper that has about two coats of paint.
1. Can I tile over the painted wall paper?
2. How about putting Kerdi over the painted wall paper?
3. Gaps between Hardi and Drywall, and combinations thereof...modified or unmodifed thinset?

I use modified in nearly all situations, except under Kerdi.
I always prefer to tile directly on drywall, not on paint or wall paper, but it's not always in the budget to remove paint and wall paper. If they are well adhered and in a dry area, you can usually get away with it, but there is always a small chance that something will de-laminate over time.

When you are going over old drywall its important to bang all the panels with your fist and check for movement. Find the studs and add some nails even if things are solid.

If I was going to the trouble and expense of installing a Kerdi shower, I would just removed the drywall and replace it with new drywall. That way you know it's attached securely to the studs, and you have a clean slate to start from.

Pete & Kman, thanks for the advice. I think I already knew the answer, just wanted to make sure. I don't want to cut corners or mind the extra work...just see if it is an accepted practice. The wife and I are going to try to remove the painted, wallpaper with this spiked, roller-ball looking thing. If it doesn't work, new dry wall.

Save yourself the aggravation and just replace the drywall. Trust me!

I hope you realize that your going to have to create a steep slope to the drain at the end and partially on the sides near the drain if you plan on having a level floor perimeter.

Based on a 5' shower area, your going to have a 1" rise above the drain flange on the short side. Hope your planning on using a small mosaic.

RC: Ripped out the drywall yesterday. Peeling paint and wallpaper was way to time consuming with less than desireable relsults. Second. That thought crossed my mind as I was putting up the CB and determining the screed line. I just have to convince the wife she can't put 2" tile on the bed unless I chiesel out the slab to center the drain...not to late to do so.

Before I chisel the slab to reposition the drain, really having had time convincing the wife on this one, has anyone done a RH drain, 32x60 (or there about) shower? And, if so, what was the slope line?

It's not really necessary to center the drain, just slope it more on the short side. You want 1/4"/foot on your longest run and set the whole perimeter at that. You could have a sloping perimeter and an even slope, but then you have to custom cut every tile on the curb and its a pain in the ass.