hollowing out coats

[rob_van_riel]

I have some figures on hand with relatively long coats. For (quite understandable) reasons, these tend to be solid, with the legs sticking out from under the solid body if the coat. I suspect this will be quite visible, and beyond my ability to camouflage with paint tricks, so I'd like to hollow out the bottom for at least a few millimeters to give the impression of a hollow shell instead of a solid block. Does anyone here have a trick up their sleeve to pull this off?
I should probably point out that the offending figures are made of metal. This can be both a bane and a boon, since the material will be quite sturdy of course, and possibly a bit flexible when thinned down.

[JamesPerrin]

I'd recommend a motor tool with a round burr fitted. Trying to remove this by hand would be a pain. Alternatively just paint the bottom of the coat black (or a very dark shade of the coat's colour).

[JohnRatzenberger]

I have a similar issue, although in resin, with a WW1 nurse's uniform long skirt. I decided to go the black paint route as the skirt is close to the ground, just above shoe-top, and I don't think anyone will be peeking.