A Customer has multi accounts

Customer A with project A

Customer B with project B

Customer C with project C

etc..

After enableing the customer portal for Customer A it isn't possible the enable it for Customer B

because i set it with an email adres for example tim@hotm.com it isn't possible to activate another Customer Portal voor Customer B with the same e-mail adres.

Or this i miss something.

This specific cutomer has 20 accounts all different invoice adresses bud all the same invoice emailadress and is run and controlled with 1 email adres.(person)

Is there a work arround?