Yeah. This gets tried. My group has tried it twice. The first time they made the portal with that in mind, but it ended up being easier just to beat the demon down. The second time Maeve just happened to be holding open a portal (in hopes of dragging a PC through), and one of them did a maneuver to push a troll-changeling through.
The problem is, it's not really possible to open a portal directly under their feet. And I don't even recall any rules that would allow you to push someone (through a portal). So it's a matter of doing it with maneuvers. And that's a matter of the DM approving it.
Plus, there's the infinite chasm rule from star wars. Any time a baddie falls down an infinite chasm (because they're so prolific in the setting), he comes back more badass and with cybernetics. Well, do the same thing, only with faerie pacts instead of cybernetics.