Yeah try it when they stop working next, you're effectively 'externalising' the relay operation by linking wires, so if it's the motor at fault, it still won't work by linking wires, but if it's the relay, it probably will. The wipers won't park by linking as described, they'll just keep running for as long as the link is there. Can't be done as an 'on the road' fix though, because pulling that connector does deprive the control unit of its main earth, so do it with engine off, keys out of ignition to minimise 'system confusion'.
Have a look what access is like to the unit/connector. On mk1 Fabia it's a pain to get at cos of dash undercover trim, but on 9N Polo and I seem to remember mk2 Fabia it's not as covered up?
I did try it on my Polo (same wiring, same control unit as mk1 and early mk2 Fabia) this morning and it worked. I got the speeds the wrong way round, it's pin 3 to pin 4 that gives normal speed, and that would be all you'd need to try I think. I see from your intro that the car's done quite a lot of miles so it might just be the motor.
Only unexpected thing on mine was that the radio came on as soon as I unplugged that connector, off again when refitted. Haven't worked that out yet.