I never used any goo in Tubulars because they weren't out yet when I was riding on them. I know Slime is worthless in high pressure tires, but I did hear from a few tubular users that Stans was great stuff as is the sealant that Tufu uses, see: http://www.tufonorthamerica.com/accessories.php
But I have no personal experience, though I haven't heard any complaints about those sealants.
But unless you have a fast sudden major blowout that blows goo all over your bike, a small pin hole which is what most flats consist of will not spray goo all over you bike because the good sealants seal so fast a lot of times you don't even know you had a puncture! I tried using Slime and that stuff wouldn't blow out of the tire hole, it blew out of the tube making a mess inside the rim, but that crap won't seal instantly and won't seal above 70psi so it's useless in road tires.
SBinNY says that there are some tubulars sold without removable valve stems, so if you want to look into sealants make sure the tubs you get have removable stems. I thought all tubs came that way today, but obviously not.