That is a wonderful idea actually!
Bulking up shouldn't be a problem, I just add some debris inside the "mouth" on the body of the mini.
However, is there some ideas for the feet? Where would they go on the model? For the arms/hand I was thinking of wrecking balls, similar to Night Goblin's fanatic weapons. I mean this is going into a Moonclan/grot army list after all if I ever pick it up ( i have some Gobbos mounted on spiders already).