One way car hire.
There's a EuropCar at both Penzance and Wick.
For the start, pick up the car wherever you are, drive to Land's End, unload as much as possible, drive into Penzance and drop the car off then cycle back to LE.
Finish at JOG, some poor soul then has to cycle the 16 miles or so to Wick Airport (there's a bus too, not very frequent though or you could easily get a taxi), pick the hire car up.
Or there's a number of other options to extend your trip a bit, the ferry from JOG to Orkney and then do some island hopping round to Aberdeen or even go round the north coast and island hop down the west coast. Obviously extends the journey by quite a bit that last option.
Specific board for this popular undertaking.
I reserved bike spaces and bought tickets over the phone. That way you can do it all at once and someone can check spaces are available before purchasing tickets. I think I phoned Scotrail for the return journey but they were able to reserve bike spaces and book tickets for the entire journey, regardless of the trains used. It was also about £100 cheaper than what thetrainline website was asking for. From the Midlands to Penzance I think I paid about £75 and then about £130 to get back from JOG. Hardly cheap but alright considering rail prices in the UK and cheaper than other options I believe.