This works for a 'hotseat' game but not for 'online' as far as I can tell.
After creating/generating a map (which you can save) select 'Scenario Params' under 'Edit'.
There you can assign 2 humans to go head to head using the 'Player' tab & 'Control' tab.
Interestingly enough, one can assign the 2 armies to the 'AI' & watch them battle it out.
I get that this is not the most efficient way of doing this, but it does work.
