Hmm...
Probably there would be an arena level area that you could import a character to. Possibly could be a big room style level, or a regular level, or maybe a maze level (but probably much smaller than a regular level--maybe half size or something). Traps, monsters on/off. Have character restrictions based on level, turncount, (or even classes) as the players like. Possibly other options, like fire from ToEF, underwater, D:49 icy, or teleport resistant, massively corrupting levels, or Andor-style shifting level.
You can set a timecount on how long you want a turn to take (as in, 1 turn on your turncount). Probably 10 seconds minimum, 1 or 2 minutes maximum. If you don't take your turn within that time, it counts as though you just pressed 5. It would still be very sluggish compared to regular play, but I don't see any way around that. You'd need to be able to connect to other player, either using server, or maybe direct IP or something.
Hoping to win with every class, doomed. Archer, Barbarian, Bard, Beastfighter, Druid, Elementalist, Farmer, Fighter, Monk, and ULE Priest down.