The interior length of a D Mag from back of switch to tail end of tube is 60mm per cell plus 24mm - 144mm for a 2D. The AA cell is 50mm and 4/5A is ~43mm. So, the MM holder has 20mm of overhead past the length of the cells (since it's designed to directly replace 2 D cells - 120mm - and the AA cells are 100mm total.)
So you've got 129mm for 3x4/5A plus 20mm = 149mm total length even if you hacked it enough to make it work. And a 144mm space to put it in. Not counting the extra 24mm needed for the spring. Your idea would require a 2.5D to work, just figuring length it seems to me. And don't forget about the resistance issues with the MM holder's springs - not a big deal with the 1331 or 1185, but still a deal of some sort.