I'm not very experience with the FV-1, but I thought I'd add my thoughts for the sake of discussion and to see what PedalPCB has to say.
If you're planning on getting the development board and doing some programming, I think you could work up a crude version of this with minimal alterations to the PCB. It wouldn't be a true favorites switch but it would give you access to one other sound. You could hardwire a stomp switch to apply 3.3v to both pins 16 & 17, which I think would be program 003? (use diodes to isolate the lines similar to the new octagon with the 8way switch). Then on that program you could set all the parameters internally, so that the position of the 3 control knobs don't have any effect on the sound. The the mix and volume controls would be the same as the 'non-favorite' mode, although I think the mix control could be routed to separate mix pot via the stomp switch).
In summary, this would give you:
A stomp switch (with LED if you like) to select a predetermined program, with no on-board parameter control, and the mix control either the same as the 'non-favorite' mode, or a separate mix knob for the favorite, routed through the switch. Admittedly this is quite limited functionality, but if you had a specific function in mind, it might be fun.
As far as I can tell, a true momentary favorites switch would require microcomputer control on the mode (pins 16, 17, 18), and the control pots (pins 20, 21, 22). And changing the mix and volume would still be a concern, since those controls are analogue. This would be a pretty cool project for a larger box, if the complexity/size/cost benefits are worth it compared to just building 2 fv-1 pedals.
Anyone else have any thoughts?