I have an application where I have a concrete ceiling which is 7' above the floor.  I need to run ~2" sprinkler branches in this area.

I can use a pear shaped hanger which will put me ~6" down.  

I want to know if it is possible to use two hole pipe straps to support the piping flush with ceiling to maximize clearance.

It is possible, but very difficult.  How do you thread the pipe together when it is tight to the ceiling?

A quick check of the dimension of a standard 2" 'swivel loop hangar' indicate you could probably get a 2-1/2" center line.  Saves you a couple inches.  Of course you still have to consider the pendent depth that stick down 3 more inches.  You probably have already considered various pipe routing and sidewall possiblities, so I can think of any other good options.

http://www.reliablesprinkler.com/system/hangers/Er...

I have thought of the swivel loop hanger.  That gets me down to about 6" to the bottom of the pipe.  I was just trying  to get it up higher if possible.

If I can use a pipe strap, I would probably run the piping slightly off the ceiling so I could make the joints.

Another problem I have is that I have to put a cage on the sprinklers.  This will add to my height that will make my piping go even lower, maybe even to 8"-9" below the ceiling.  I want to use an upright head so that I can keep the sprinkler as high as possible.

This is going to be a real head bumper.