Yes it is possible:
In the multiplayer screen, under game mode, select "Load Game", select your save file and wait...
Then change the game type to "Play be Email". Then, launch, and it should play as a regular PBEM. You might want to set the turn timer to "none" before you start, other than that, there aren't any settings that can be changed.
However, it is worth noting, that it does not allow you to password-protect you civ as in PBEM's from the start, as it does not ask you for a password. And also, any human civ's in the LAN game have to be filled with human players by PBEM, you can't swap civs between AI and human, basically.
Hope this helps!