Assigning bloggers in specific user groups to specific blog categories options

Hi

Could you advise as to how I assign certain Joomla user groups to certain blog category options?

I'll explain some more. We currently allow a certain group of our website members to create blog posts. We only want them to create blogs under one of the 16 categories and so far they've done so without any problems. However, they do have to select the category from a drop down when they are writing their blog post and it would be much better if we could limit their options to the one that they always want to choose. So far this hasn't been too much of a problem because there isn't a huge number of them but soon we'd like to open up the opportunity of blogging to 1000's of the members and so the scope for them selecting the wrong categories is large.

Is it possible to restrict the category options that bloggers see when they are adding a blog through front end editing - according to their user group and if so, how?

Thanks

Jamie