I have successfully mounted a CLAMcleat (i.e. not a cam cleat) behind the netting in the RHS tray; this worked extremely well and the small size of the clamcleats is much more appropriate for a kayak IMO. The one I used had a shim - which lined it up beautifully with the incoming sheet and a keeper which prevented a stray line from catching in the cleat and made adjusting it a breeze without compromising my ability to release the sheet in a hurry.
lately I have found that on the Adventure you don't really need to install a cleat to belay the sheet because you can achieve very nearly as effective a 'lock and release' mechanism on the standard boat. The way it works is as follows:
By the way, this solution depends on a couple of things - firstly, the sheet needs to come to the helmsman's right hand via a turning block in the front cockpit area and the lead needs to come across the top of the gunwale of the boat. Secondly, the method probably won't work if the sheet is too thick (or too thin, I suspect).
On the RHS gunwale of the Adventure somewhere in the vicinity of/under the helmsman's hand there is one of Hobie's tiny little black plastic cleats. The lead of the sheet should come down the gunwale to that cleat. Basically all you do is take a couple of turns of the sheet round that little cleat (not figure of eight; just round it - and the sheet needs to be thin enough that you can just get two turns round it - but not too thin... see below) and put a loop in the bitter end of the sheet which you tuck from left to right under the sheet in front of the cleat (there's a kind of 'knuckle' in the moulding just in front of that cleat and the pressure in the sail puts just enough tension in the sheet as it passes over the knuckle that it will grip the loop and hold the sheet more or less fast on the cleat). Without the loop-under-sheet 'lock' the cleat does not provide enough grip on the rope and the turns will just slip on the cleat - but with that little bit of extra grip it works pretty much perfectly (and my theory is that as wind increases, so the tension in the sheet lying over the loop will increase with a consequential increase in the grip - but I haven't tested that in properly strong winds I have to admit).
In my experience this provides quite enough friction to lock the sheet in 'normal' sailing weather and if you hold the end of the sheet it can be released almost instantaneously by pulling sharply upwards whereupon the loop is pulled out from under the sheet 'lock' and the two turns will lift cleanly off the little horn cleat with a bit of tug on the line (hardly noticeable tug in my case as my sheet is not too thin so as to really catch on the horns of the cleat - if the line were thinner there may be more catching on the horns).
To adjust the sail just pull the loop out and either let some line slip or pull some line in and then remake and reset the loop lock... perfect!
I know a picture would help... I'll see what I can do but I haven't mastered this uploading pictures business yet