Starting Applications using IShellFolder + ITEMIDLIST (relativ to IShellFolder)???

I just tried a lot of things to start a file from ishellfolder, identified by an ITEMIDLIST;
but there are a few problems:
I'd like to get the Path (no need, if u have other suggestions, please reply!) and then start through
ShellExecute, or ShellExecuteEx; here's how I tried to get the path:

SHGetPathFromIDList(...) just works if the known ITEMIDLIST is complete.
the one I have is relative to my IShellFolder - Object, so it only works with objects in
the control panel (not a subfolder!)
if i use GetDisplayNameOf(IDLIST, SHGDN_FORPARSING, &string)
this works fine with Network - Resources, but the control panel and any other special folders
don't want to work with that.
I'm desperate.