I think its possible. You may spend more points than you want on keeping your slann alive, but you are saving points by not buying a TG unit.
Solo Slann:
Ethereal,
Know all Lore,
Free Dice,
BSB,
Cupped Hands
That should get you by and only for 445 points. The ethereal will save him from cannons and he still has all the firepower of a "normal" slann.
The only threat to this Slann is static CR. If he gets in combat he is prob dead as most things hit on 3s wound on 4s. This is the only threat to a Solo Slann. You could give him warbanner or terror to either help CR or to stop units attacking.
I think this ed has more opportunities for a solo slann.
Also is it possible to stick a Slann in Saurus. I thought that would work last ed, does it work now?