If your AVR will support them, you could always experiment with Front Height and Top Front (or Top Middle) as a combination in a 5.x.4 set up. You do not have to install tops in the ceiling but can mount something like the SVS Prime Elevations at the side wall/ceiling junction, aimed at LP, and as close to possible in the front-to back placement as the in-ceiling options per Dolby's recommendations.
All that said, how big is your room? Layout? (Photos are always helpful for this kind of thing.)
FWIW, I tried running just Fr.Ht. for a while and was unimpressed. If that is your only option and you want to experiment, no reason not to...
I would, however, recommend putting forth the extra effort and make certain your bed layer is the absolute best set up you can. The better your bed layer is set up, the more luck you will have with the overhead speakers.
Oh... and avoid those Bouncy-House Atmos Modules that are supposed to reflect off the ceiling.
For those to work properly, you must have perfect geometry for those sounds to even have a chance of giving you a decent quality almost believable bubble of sound.