There is a glue called PowerStick, used in a caulking gun. Wilder's in Raleigh, NC has a display of it holding boxes, straps, rods, etc. to a cinder block and a large boulder. It may be worth a try. I bought a tube of it a long time ago but someone borrowed it & never returned for me to try. Check it out at powers.com or Google powerstick adhesive.
If your conduit can stay in place long enough for the glue to dry, this might work for you. I would not use it to anchor an entire system, would maybe drill anchor the boxes & glue the straps. See if customer would go along with it.
I once saw a concrete ceiling with some type of strut embedded in it. I thought that would be handy to do with Unistrut.
