Firstly, I would love to know how big exactly that sig is, I've made wallpaper that was 1 meg.
Secondly, no the mods won't make an exeption for one person because it would end up with a domino effect of people askinin why they cant put 1 meg sigs in.
My biggest sig is 27.2kbs and this one I'm using now is 11.6kbs, so I'm betting yours is a .gif. Convert it to a .jpg and i garantee that its size will shrink dramatically.