What is the normal working pressure? Just city water main pressure?
What's that, about 50 psi or something? Probably no need to exceed working
pressure and a bad idea I would think, if you are leaving the heads in
place. The other idea, if there is water in the section you need to blow
out, is just to ease on the pressure gradually and watch the water flow out
the drain at the other end using just enough pressure to do this. If it's
a fairly flat run between the two point then only a few lbs would probably
do it. If you have verticals connecting floors then a bit more.

Is there a way you could push 50/50 antifreeze/water solution through the
affected area so it could just sit there?

This is just reasonable speculation. Maybe someone more knowledgeable will
know for sure.