I extended my PD remote cable by cutting it and splicing in a section of wire, in my case cat-5 network wire as that's what I had handy to work with. Any straight-through wired extension should work just as well.
I don't know offhand if it's a serial digital interface between the two or just two wires directly wired to the pushbutton switch and two for the LED indicator. If it's the latter, wire length and type are pretty much immaterial (at least within reason--miles of wire might pose problems). If it's the former, it's conceivable that the wire characteristics might matter somewhat, though it doesn't appear that they use anything at all special like twisted pair wire. For modest lengths, it's an academic concern anyway.
For people thinking of flush-mounting the remote: take note that the top and bottom of the remote pendant case (at least the current version of it) are rounded off, but the sides are cut pretty much square. The basic result is that cutting a basic rectangular hole in luan or whatever for it tends to make the gap at the top and bottom look bigger than at the sides. If you're not too much of a perfectionist, it doesn't really matter much. I suspect undercutting the top and bottom carefully would avoid this possible annoyance.