You would deal with the fee as you would a normal PayPal transaction - for every 1 transaction, you create 3.
Take a look at this guide:
http://help.quickfile.co.uk/main/1/how_do_i_handle_payments_from_an_online_payment_provider_like_paypal_.htm?searchTxt=paypal&criteria=
Also worth having a look at this topic too: