One time I had Edwin solo that lair - it seemed easier than having a party of six actually, because there were less people in the way.
Of course he had Staff of the Magi, which pretty much makes you invulnerable to beholders if you keep equipping it
... with enough fireballs/cloudkills in her book or wands, Nalia ought to be able to clear it out by herself if she has the Staff, in fact Edwin did the whole lair without a rest, but he was pretty hi-level.
I also try to get the illithid to help clear out some gauths if possible by getting them mad at each other [img]graemlins/hehe.gif[/img]
If I didn't have the Staff of the Magi for my mage, I'd probably do the polymorph self trick if I wanted to do it the easy way - again, sending your mage in alone might help, otherwise the beholders will attack the other (more vulnerable) members of your party nearby if your guys try to start a fight