Signature Resize on Active Images

[AskaLangly]

So I have a signature I want to put up; one from Wiinnertag. Its size is 500x175, and as you all know it's active, so when I play a game, it gets added (just like the XBL/Steam cards and anime-planet, for when I update my list). Sad thing is, if I resize, it's passive, and there is no automatic resize. Any help? Thanks.

Edit: Also note my signature. Fooling around with syntax until there's something suitable.