One possible solution maybe to :-
Use an external video editor to compile your green screen walk vids into a continuous single file. If any capture a “walking on the spot” cycle you may be able to edit it carefully enough to create a “minimum glitch” walk loop. If so, cut and paste this several times within your editor to create the longer walk sequence your scene requires.
After export from your video editor, process the single file through popVideo converter and apply to a billboard or plane in Iclone.
A little trial and error is required to avoid foot sliding effect. In the time-line adjust the speed of the plane you animate from left to right for a “best match” with the “walking speed” of the character in the popVideo it is displaying.
Geoff.