Draw random stuff with PHOT while the game is paused. Then, going to the console, type
!set vx phot a
!set vy phot b
!set life phot 0

where a is the x-velocity of the PHOT and b is the y-velocity for PHOT. For immobile PHOT, set a and b to 0. Setting its life to 0 simply means that the PHOT won't suddenly disappear after a while, though you can monkey with it to create saves similar to those BRAY animation saves.

You can do the same with ELEC but not with NEUT as it tends to disperse after a few frames.

Note: ELEC has some rather funny properties when you try to pass BRMT through an immobile chunk of it. Also, immobile pieces of ELEC and PHOT have interesting heat transfer characteristics.