Temporary toilet installation
Any "temporary" installation of a toilet should be treated as a permanent one.  That means if you need to temporarily build up the floor, the temp floor needs to be securely anchored to the sub-floor and the toilet securely anchored to that temp floor.  

If you do not install the toilet as if it were permanent you risk the release of raw sewage onto your new construction materials.

Brick and mortar, as Chris said, seems overkill.  Secure some wood to build up the floor to the proper level and secure the toilet to the flange as well as the flange to the pipe.  

This may result in you having to redo some plumbing around the toilet, if, for instance, you find you need to remove the flange to install the floor, although generally you'll cut the floor around the flange.