FX-style summoning
Possible, but ungodly complicated. You would need two switches: Summon and Dismiss. You'll need to make a "Summon" switch for every summon you create. Make a character of whatever summon you want, giving it its own abilities (including a "Dismiss" skill). Then make a skill named after that character, and make it a Switch type (activating the proper Summon switch).

Make a common, Auto-Start event triggered by the Summon switch to remove the summon from your party, and replace it with the party members. Then, turn the Summon switch off.

Now you need a common event that has to be called, named after that summon. Set up the event so the actions look like this:
Change Party: Remove- (all members)
Change Party: Add- Ifrit (or whatever)

Also make one for dismissal
Change Party: Remove- Ifrit
Change Party: Add- All Members (to simplify things, make it so you can't learn summons until all avaliable characters join your party)
Change Switch: Summon- OFF Set
Change Switch: Dismiss- OFF Set

Now go into Monster party, and set an event page to be triggered by the switch "Summon", calling your first common event. Next, make a second page triggered by the switch "Dismiss", calling the second one. If I didn't leave out anything, you should be all-set.

Umm... You get all that? This method will make it so that the Summon gains its own Experience Points and levels up in that way, and means that if the summon dies, it's Game Over. Nothing can be done about that, not that I know of.