Multiple email fields on 'Create Account'

[ultras.nick]

I've searched in contributions, but I was not able to find any :(

 

Here is what I want to do:

 

Currently when a user creates an account on my shop, he is obligated to fill an email adress.

 

I want to giv him the possiblity to introduce 5 emails - here he should fill his friends emails - so he can recomand my shop when he creates an account.

 

I also want to keep those mail adresses on my database.

 

Can someone help me with this?

 

Thanks in advance.