I've read on here that unless the e-commerce shop has a payment portal the default position is to email the prospect purchase details for further manual transaction. However if I set up a site using Sagepay (UK Payment Portal) but still wanted some customers who trade on a monthly credit account basis to use that (email) as an option, is that achievable with the e-commerce add-on or does it mean hacking into it to do some serious modifications?

I tried a UK based concrete5 site with a shop to test my hypothesis, but when I get to do the payment side it only let me continue through Sagepay, so I'm thinking that if you have such a gateway enabled does the email option disappear?