You normally can't nominate current map on uncletopia but with a script you can make it happen.
For instance, when playing on borneo you can nominate borneo again with a script like this:
alias "+nominate" "say !nominate pl_borneo; say !nominate pl_pier; say !nominate pl_upward; say !nominate pl_badwater"
bind kp_5 "+nominate"
The server will spew out a couple of errors but after that borneo will show up in voting and you can play it again if people vote for it.