I think you want to use !PopupDynamicFolder [somepath] as a regular bang.

e.g.
!PopupDynamicFolder "$CommonPrograms$|$Programs$"
or
!PopupDynamicFolder "$ThemeDir$"

Defining multipopups with custom entries is done like:
Traditionally "!howDoYouWantToNameIt" begins with "!Popup".
e.g. "!PopupWhatYouWantToNameIt"