What's the best way to spawn an actor using an archetype from a parent class?

If you try to spawn an actor using an archetype from a parent class, you get this error:

Do you know of any way to force the actor to spawn if the template class is a parent of the spawn class?

The situation is modding in my game. I would like players to be able to extend my GameInfo class, set their own default pawn class, and then have the game replace my pawns with their pawns.

Any ideas? Thanks for any help you can provide.