You can also clear lava with the tornado spell and place non-burnable items like hammers on the vents. A character with the scoundrel skill "winged feet" can run over lava without burning. Can't be more specific as have not done the source temple yet, sorry.
I got stuck on this part too. It is on the way to the Alchemist in the temple of the dead for cassandra's body.
There were no vents, statue would not respond to invisibility, tornado no longer removes lava, BUT your suggestion about winged feet DID work!
