It did involve taking my router out of the table, mounting a new baseplate and fitting the guide bush which is a bit of a pain but cheaper than buying another router.
I'm using the microjig dovetail bit / clamps all around my workshop and find it a decent holding method. Here's the vertical panel to hold the piece being morticed.
The only real issue is the bit where you fight to get everything lines up and the clamps tightened but I think once one board is set up I can mount some stops in the traks to make it easier.
..And of course, to show I managed a mortice. (18mm x 5mm by 15mm deep if you're wondering some of you might know those measurements

I know it's not rocket science, but I've been meaning to build one for about 4 years now.