It's possible, but you need a comprehensive IE modding tool. In the .CRE file for your party member, set the portrait to use a static .BMP instead of an animated .BAM file. You'll probably need to extract the appropriate frame out of the BAM first, though. (BAMs are just a bunch of BMPs grouped together.) Change the portrait field to use your new .BMP, put the .BMP and the .CRE in the override folder, and there you go. Note that this won't take effect if you've already encountered the party member. It also means their portrait won't change as they get wounded.
Near Infinity can do this quickly and all by itself, and it's pretty simple, actually. The user interface takes a little getting used to. You can download it from Sorcerer's Place. Alternatively I can make them if you really want me to.
EDIT: Apparently the portrait HAS to be a BAM file, but it can be a BAM with only one frame in it. So that's a bit more complicated, as you need a BAM editing tool also.
Post edited December 09, 2011 by bevinator