default user in blog templates

Hi,
I am allowing users to sign up for a new blog and marketpress store with Blog Templates and I would like to have their login not be as an admin but as a custom role. I have tried role scoper and others but it seems that it doesnt quite work correctly unless i manually add a new user.

Is there a customisation or plug available? or is there someone who has solved this issue previously? I have looked through the forums and there seems to be limited succcess in this.

Thanks.