Thanks for your replies
What I did was copying the "potato" weapon file from SP to MP and changing its name to "potato_mp". Also I changed the sharedAmmoCap value from 4 to 3 (since cod2 throwed me an error) and the values of the potato's bouncing to make it funnier
The result is this:
http://classic.xfire.com/video/62f4c6/
I should lower the bounce a bit though xD
Thanks guys