Anchoring 2D animations?

Hi, here's a problem I'm having. I recieved a number of 2D animations from my artist this week, but while the character in the animation is the same size in all of the animations, the Animation itself is arbitrarily larger/smaller depending on what the character is doing. Sometimes he needs more room horizontally if he's throwing something, sometimes he needs more room vertically if there are stars coming off his head, etc.

Naturally, if you try to swap in one animation for another without resizing, the character looks funny as his new animation is being squashed in to container which is an unmatched size. Also, since he may be in a different spot inside the frame, he also appears to teleport forward or backward with the swap.

Short of going back over every single animation and resizing them all to have exactly the same frame size, does anyone know a way of "anchoring" the character and making this situation tenable? Thanks in advance.

-Eric