DO NOT DISTURB, I'm testing

At my work, I’ve recently introduced Session Based Test Management (created by James Bach). It has been piloted in an Agile project. I could be biased, but I think the pilot is working extremely well. There are lots of positives from it, which I hope one day to share, but there’s one thing we’re struggling with so I thought I would come up with some ideas and then open it to the rest of you for your suggestions and comments.
The problem is that when a tester is in the middle a testing session, it’s best if they are not interrupted. But with all the talk on being collaborative, the testers are getting interrupted all time. I need a solution where testers remain part of the team but are left to do testing when required without appearing rude. Please let me know your ideas :o)