Car seatbelt falling into rear seat cracks! How to fix without a seatbelt extender?

Hi all, we have a Clek Olli in our 2009 Subaru Forester. The Clek fits great and positions our nearly 6yr old (48lbs) perfectly, and we LOVE the seat. Our problem is that the rear seat belt falls back into the seat cushions anytime you reach for it to try to buckle. This is an issue both for our son to try to buckle himself in safely, as well as for us when we (inevitably) have to buckle him in. We took it to the dealer and they said get a seatbelt extender. Now I know that seatbelt extenders change the position of the belt on your child and are not considered safe nor are they made for use with children's carseats. However, I am at a loss with what to do. We really don't want to get a different booster for our son - he loves his seat and we really like it too (for the first time in 6 years we can actually have three people in the back of the car). It's not an issue with seat width - we can all reach the buckle just fine - but the second you grab the buckle and try to buckle it, it slides right back into the seat. Does anyone else have this issue? Has anyone solved this? We keep thinking that the best bet would try to jigger something up to wrap around the seatbelt stem, but have already tried cardboard and tape and it didn't do anything. Any idea!? Anything would be appreciated. This is driving us nuts!

You can try a small piece of pool noodle instead of a cardboard tube around the buckle stalk. Just cut a segment off and then slit it. That might help!

[ame="http://www.amazon.com/My-Buckle-Mate-Color-Black/dp/B00LI151SG"]Amazon.com: My Buckle Mate(Color=Black): Health & Personal Care[/ame] I like this, it's kind of tallish, I've tried to get one into an Aveo and the buckle stalk was a little too short, but it's definitely sturdy and I liked it better than the pool noodle I tried in my car (though pool noodle and lots of duct tape DID work for me, it got a little gummy from time to time, but it's free at least!)

I would honestly consider taking a big darning needle and embroidery thread and making big loops around the seatbelt (so that it doesn't actually pierce the webbing) and sew the buckle to the edge of the crack. Not enough to be strong enough to withstand a collision (I'm not that good of a seamstress) but just enough to keep the buckle from running away.

Thanks all!! I will try the pool noodles and see how that works. Man, it is driving me nuts!