hong: you sure are crazy. Is there ever an argument you do not think you have won?
Rel:
As a general tactic, if the wizard had ranks in alchemy, and/or Know (nature), then extracting poison from a familiar in quantity enough to poison arrows should indeed be a possibility. We are talking about geting enough in a melee, coating an arrow with it, and firing that arrow.
The medusa has MANY snakes to get the poison from, while the Wizard has but one. Also, The Medusa's snakes are readily avaible and do not require her to take up a hand holding them - she could essentailly "run an arrow through her hair". AN unusual tactic, but a fair one - AS LONG AS IT TAKES ENOUGH TIME. The wizards snake familiar would have to be held, or at the very least come out from whereever he was kept. If the familiar was already out in the open, then he could be attacked in melee by savvy opponents.
Also, just becasue a special ability is not supernatural does not mean a PC should possess it. Some are simply very valuable (like being large, or having darkvision 90' rather than 60').
As a visual, I can see a swarm of snakes squirting thier venom a few times a day on an arrow, but I cannot see a wizard milking his pal in combat.
Maybe I'm unreasonable.