Manually adding members with recurring subscriptions?

Our client is going to set up a subscription-based site where people will have to "buy" accounts and be billed recurrently (and have their accounts blocked if they don't pay). Right now it looks like e-Commerce is going to do this swimmingly. However, aside from taking online orders, the client also wants people to be able to send in a check, at which point he would manually create their account in Drupal. So is it possible to mark a manually-created account as an account that e-Commerce should manage and block as if it had been purchased through e-Commerce?

I'm not afraid of doing a little PHP hacking of my own to get something like this to work, but if that's the case, any guidance as to which database tables and columns I should be looking at and so on would be appreciated.

Thanks in advance for any help you may be able to provide.