Michelins and Vittorias have removable cores. The Vittoria extenders work well of you want that type. I have also used the Topeak ones that go over the top of the valve and I like those also.
Thanks for this reply, exactly what I was looking for. I wasn’t sure about the Vittorias because I had heard they worked with 808s which have an 82mm depth.
Not all conti-tubes come with removable cores. The nicer race ones do. Then the tufo valve extenders are really nice, and you can stack them (two 40mm would be plenty) to get enough distance. Then you’ll be able to use the tube as normal and won’t have the leave the valve unscrewed within the “over” type valve extenders.