Say I make a 64x64 pixmap then save it. The pixmap could be broken down into 4 different tiles of 32x32 size, then be given x and y co-ordinates then saved in a different portion of the dmi's data bank with named arguments named on the basis of the icon state's position in the dmi( index wise ), with an extra number at the end separated by a delimiter defining the number of the tile, so the tiles could be indexed again later. These tiles could then be hand-picked for use in image() and icon() procs with an extra argument referring to which "tile" of the selected iconstate we want.
Example:
I make the following 64x64 pixmap and want to save it. I give the iconstate the name of "yeti_print".

The pixmap is broken into four different tiles of 32x32, these tiles are saved into a portion of the dmi, being named relatively to the yeti_print iconstate.

yeti_print:1,1

yeti_print:2,1

yeti_print:1,2

yeti_print:2,2
Now say I want to get the tile of co-ordinates 2,2 from the iconstate of yeti_print using a proc. An extra argument could suffice as a means of locating the tile relating to the wanted co-ords.
image( icon='yeti.dmi', icon_state="yeti_print", tile="2,2" ) would return

A syntax for implying iconstate tile selection in the icon_state variable could be written as icon_state = "yet_print:2,2", or in a list such as icon_state = list( "yeti_print", "2,2" [other icon options, such as dir could be listed in this list too] )
I myself haven't used multitiled icons, so the format of the icon states DM generates could be different. I think it's a space instead of a colon, though.