Different user email registration rule for different roles

Maybe this as already been answered somewhere else but I don't seem to find a solution for what, seems to me, is a quite basic and common situation related to the user registration workflow. I'll try to explain it.

During a regular user registration the new user can choose one of two roles: "Professional" and "Reseller".
The Professional will receive an email with the link to set the initial password and login imediatly onto the site. This is handled automaticly by the system.
The Reseller will receive an email with the indication that his registration is pending the administrators approval. This has some "manual" intervention.
It happens that I'm not able to have both situations setup as one blocks the other. I've tried the LoginTobogan module and also the solution in this discussion both without success.
It looks like it can be really simple with the implementation of Rules, but all falls appart because it is not possible to turn off the automatic emails from the system. This causes the new user to receive more than one email, thus leading to confusion.

Is there a way to make a custom workflow, where each role can have a particular tratment, bypassing the system registration one?
I've read some possible solutions using the hook_mail functions, but I'm no programmer, so another way out of this would be great.