How do I use my own files for AIM expressions?

when i send an IM to somebody, they hear the default aim sound. i want to change that sound to another file i have on my computer. any way i can do that?

and i tried going to SETTINGS and then SOUNDS. this only changes what i hear on my own computer, it doesn't change what i send to other people.

when i go on aim expressions, the sounds they have are very limited.

i can change my buddy icon easily, but i don't know how to use my own sounds that i made.