Well, in battle mode when you die you have to wait, sometimes for a long time.
So here's some idea:
Place a second map below the main battle map (or in the areas you can't see anyway). People who are dead then spawn in this second area and can play again while the real battle goes on - with no gold boni, effect of the outcome of the real battle or scores, just for fun.
It could be any mode actually, setting up a dueling area would be really easy. Just some giant carpet/hall/arena under the map where people can spawn on (possibly even created by a single script for every map), and you can spawn them 10 seconds after they died without worrying about how to mass spawn.
Well I don't know if that's possible, but think about it, if you could duel while getting xp and in dead time anyway that would be awesome. If you don't want it you can have a checkbox to disable it or just stand around.