Wow I'd love to be proved wrong here, but I guess that won't happen for quite some time now. While I'm at it, I just might cancel and redo my spend credit because of this:
actually they only covered me 5 ads even when Avix and me got the kaho the same day, they charged Avix for the first customization
Same day even? Wow. So I guess refreshing my spend credit would mean since mine got submitted later that the other person will have to pay 15$ and I'll only have to pay 5$ eh? Nice, that sounds fair to me 
I don't think it'd ever be quite fair. If you just wait a day for the person to get theirs, and then put it in, wouldn't it be the same thing as submitting soon after? What it comes down to though, is you finding out about them having placed that $15, and then discussing it with them to split the cost.
I'm a bit at a loss though, because either way if the GM were to tell the other person that say for example:
Hey, Praeline, Freestyle is getting the same kaho customization as you, would you like to share the cost with this person?
Isn't that also, divulging information? @_@?