Yeah you can glue it like that, it will plate outward, and after a little bit encrust over where you attached it on the back side. It will help it to encrust over the attathement, if it's not an absolutely vertical rock face. A place where it is slightly angled towards the light above the attachment will help it encrust onto the rock ( needs the light). If its totally vertical w/ no direct light at all, it will take longer to get it to encrust onto the rock, it will still plate outward, just be much slower on the backside. I glued a of about1-2" in this way when I moved into this tank 14 months ago and now it's about 8" on the rock side and 7" in radius, shaped like a half moon.
Love Monti's but when they're growin good, you do a lot of rearranging. Right now I think I'm going to have to trade a small dinner plate sized one as its shading some prime real estate ( the one left of green Hydnophora in one of the pics). They're really pretty easy, just don't let them get stung.
Good luck...sorry about the delayed response...at work.