Ceramic Shower Seat

Tim,

I'm going to be installing a seat in my custom shower but there is one thing I can't figure out. If I run the membrane up the front and over the top of the seat and cement backer board to the top of the seat how do I attach backer board to the front wall of the seat without screwing it through the membrane? My seat is the same width as the shower so I planned on covering the the front of it and overlaping the side walls a few inches with membrane.

Thanks in advance
Steven

Great question Steve... anyone have an answer? Tim?