the easiest way is to buy a blank adapter made for the gun. The Finns made them up and apparently used them. Northridge had some at Knob Creek a few years back. You might check their website along with numrich and sarco. If you can't find one it is possible to make a new orifice for your standard booster that will restrict the gas flow enough to operate the gun.
As for blanks you'll just have to see whats out there. Most machinegunners don't shoot blanks so we don't know who has what and which work best. I have never seen wood or plastic bullet blanks for the 54R and this means you'll likely have to come up with some sort of adapter for the feedblock to keep the blanks in the correct position while feeding and exclude live ammo. There have been many different types of military blanks imported so something should work.