Avocado is AMAZING on everything!!! Especially on veggie burgers... mmm. My mom always reminds me how fattening it is and I just have to go "SHHHHHHH, I'm enjoying it!"
I think rubber cement works perfectly for me (: Is masking fluid (what's it called?) more expensive or cheaper? I can't seem to find it at one of my local craft stores; maybe I'll have to check another... hmm.