My recommendation is to use brass, copper, or aluminium pipe instead, the kind modelmakers use. (Here in Finland, I've bought this stuff from HobbyPoint; something like 3mm to 5mm outer diameter and half a millimeter to millimeter wall thickness. I actually have some of this stuff on hand right now.)
The tricky thing is to use a dremel with a cut-off disk or two to cut a 1.7mm to 2.0mm wide slot lengthwise. A hacksaw may work even better, if you do a quick jig out if wood with pre-cut saw slot at ends, pipe held in a groove between the ends, and a high-TPI blade with a suitable thickness (including teeth set; 1.8mm or so should be relatively easy to find). Put a bamboo grill skewer or something inside the pipe while cutting, to both protect the other side of the tube (so you don't split it) and to avoid deforming the tube with too much pressure. Gently file the burrs off using a small square or triangle file.
That gives you a round C channel with the opening at about 2mm. However, the shape is such that you can easily clamp it closed. If the length of the C channel, outer diameter, and wall thickness is right, you can use normal alligator clips as clamps. The outer diameter of the pipe only affects how deep the PCB will sit inside the channel; the idea is to let it seat all the way to the back inner wall of the pipe.
If you don't have the tools or the time to do it yourself, contact your local Hackspace (mailing list or forum) and ask if there is someone there to do some different pieces for you for a reasonable price, explaining the use case. Reason is not that hackspace people like to do commissions, but that this kind of tool is something I suspect a lot of hack-makers would find useful and interesting, too.