you could bend some 1/8 by 1 inch alumimum bar stock into a shape then screw and glue it to the bottom of the grip and on the rear of the pistol
might also need a reinforcing bar inside the shape as itll be a tad flexible
if you have a cad program and a 3d printer you could print the part instead of alum barstock
you could also use some shaped spacers and screw on a pignose adapter for a AR collapsible buttstock.