Hmm...first, unless all of the other lights are out on
stage, this will
not work, unless it's just painted on to a surface and the
blacklight is used to make it appear on that surface (wall, box,
etc). It will not work if the cat is a physical object. Now that I've covered the way too obvious which you probably already knew...
Get blacklights. Don't use
gel, get the real thing. If the director wants it that much, they're gonna have to rent or buy. If you're in DC, it should be easy to find a place to rent Blacklights.
I think that the question that you should ask is "how much UV will
tungsten bulbs put out anyway?" and I can't answer that...but I still say go with the real thing! Get an
Altman unit on rent or something like that.