Freelander Tick-over Speed

I run a gliding club and we have been given a 2002 Freelander Diesel manual for airfield use. However, even in first gear, it will not run slow enough to tow a glider at walking speed. We have two Discoveries and they are fine in 1st gear at tick-over speed, but the Freelander is simply not quite slow enough.
I need to slow the tick-over by about 100 rpm. Is this possible?

Couple of suggestions:

1) Fill the boot with concrete slabs.
2) Put smaller tyres on it.

At that speed why not pull handbrake on a couple of clicks? Don't know of a way of altering it unless you redesign the throttle pedal arrangement and maybe change the resistance as it is drive by wire.

I think it's possible to reduce the idle speed using T4. However this option is normally reserved for a dealer to "tweak" the idle to eliminate a particular vibration from a vehicle at the default idle speed.

Alternatively buy an automatic instead, which can go as slow as you want.

Another very expected way would be to convert it to electric, so you can drive at any speed you like.