I personally find it a real niggle that you can't raise the rear shelf from the inside without opening the rear hatch. It's a pain when you're sleeping downstairs but then have to pop out of the van to get something that's just under the shelf. With the door closed there's no room to raise the flap, even if you could get your hand to it.
I wonder if it's possible to come up with some sort of release mechanism that would work from the inside without removing the locking facility altogether?
There are two parts that lift up:
The heavy support frame that requires turning the knob which cannot be released from inside. This supports the canvass bag if it hasn’t been put in the loft or thrown away! when lifted this frame is not self supporting and moves upwards as far as the back seat. You need to do this to get at the jack etc.. Mercedes expect you to hold it up with a strap they provide wrapped around the right rear headrest. This is how I managed to drop mine and break the knob!
The second is the upholstered bed base that contains the outside table and raises up to about 45 degrees on a ratchet.
If you want to sit up in bed without going outside you could attach a strap ( or the one Mercedes provide) to this and bring it inside. You can then pull the mattress to read in bed etc. without going outside. Needless to say you have to pull it up to its uppermost ~45 degrees before it will lower.
I have checked this works in principle by attaching a stap to the stored table under the mattress support. I don’t recommend doing this as a permanent arrangement because it will put a strain on the table legs or the retaining clips - both prohibitively expensive to repair or replace. A more permanent arrangement attach a strap under the rubber pads each side of the bed frame or bolt it to the frame.