For a quick 'side of the road' solution .. many moons ago in my '79RRC whilst on a drive up to Ayres Rock, I had the same idea.
Just past Pt Augusta, got tired of the right foot in the one position and would 'lose blood - numbness'.
Pulled up and looked at what I had and what was around the roadside stop whilst on a break.
I used to carry with me a small trolley jack(1 ton) in case was needed. So it turned out that the removable handle they come with was the perfect length to use as a jam between the RRC's door handle and the accelerator pedal.
So drive from just outside Pt Augusta and Uluru then back home using the jack handle(ie just a tube) between door handle and pedal. Worked a treat.
When I got home I fitted a spare Zemco CC that dad had sitting there for years .. easy install.
As for a proper solution I can recommend Commands products(good customer support)
I currently have an AP500 in my D1(tdi).
I looked at the install instructions before committing to buy, to see how easy the install appears to be, and I thought some of the concepts were a bit beyond my pay grade.
But as it turns out, they weren't.
Got a mob to install it(not cheap), and they basically stuffed it anyhow. Looping the cable too tightly, and soldering the LED indicator so that it was impossible to remove the dash if needed(which of course I did!) 
They used the most pathetic setup on the accel cable, that bent itself, rather than actually pull on the spindle.
So, needing to basically redo most of their install for the CC system to actually work properly, I soon found out that install was a lot easier than I imagined having read the install data!
Anyhow, maybe a year or so afterwards the cable between the electric module and the accelerator linkage snapped at the electric module end.
Easy to figure out and find and fix.
Called the distributor to get info on where I could buy the cable, and he said he'd send me one.
Couple of days later it came.
ie. good customer support.
My main interest in the AP500 was that it came with the option for a wireless remote switch(and that it was electric, not vacuum) which I mounted on my steering wheel(via a small bracket I made) .. easy reach and non intrusive.
The only downside with the AP500 is that it doesn't have a 'coast' function, so you can cancel the CC momentarily and then resume at the last set speed.
It only does OFF, then ON and resume. One extra button press hasn't yet killed me, so I got over this negative quickly anyhow.
Note I use my CC 'all the time' .. basically 99% of my driving time .. traffic or no traffic. I have a bung right knee and for lack of a better description .. I need it!
Other than the cable which broke due to the idiot installer making the loop wayy too tight .. never had any issue.
But .. for the OP on his current drive around the country .. just cobble something up with whatever stuff you have at hand.
Arthur.
All these discos are giving me a heart attack!
'99 D1 300Tdi Auto ( now sold :( )
'03 D2 Td5 Auto
'03 D2a Td5 Auto
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