The vast majority of the "on bump stops" that occur are software related. An incorrect signal (failed height sensor) or other electronic fault causes the system to shut down to prevent it from damaging itself. Rarely does the hardware fail. (Well expect the recent events relating to control arms contacting the airbags).
First you need to understand the system and the failure points to come up with a solution for each type. But to quickly answer your question, the only reasonable way to get at the internal bump stop would be to attempt to cut off the bag and wedge something in there, but you'd need to do this for all 4 bags and that equals over a thousand dollars of new airbags.
So for software related issues, a faultmate can help you reset the system to get it to start up again. If the system has failed and you still have air in the bags, you can pull a couple fuses to shut down the release valves from opening, thus keeping you up until you can get off the trail.
Assuming the bags, lines and valves are fine (which is a lot of the time) - I am in contact with a company in Australia which is in the final testing stages of an "emergency air up" kit. This involves placing some valves in line for each airbag. If the main compressor or software fails, you can use a small external compressor to manually inflate each bag. I have a thread running on
www.lrrforums.com with all the info, but the site is down for maintenance so I cant link you to it.
In all honesty, there is no 1 good solution to this problem. You need to be prepared for a failure of the computer software system, the compressor, a bag, a height sensor, a air line (splice kits available to patch the line), etc.
I would suggest reading as much as possible on the following forums:
www.lrrforums.com,
www.landroverworld.org, and disco3.co.uk.
This is a good thread:
http://forums.landroverworld.org/showthread.php?t=20014
Ok all that said, I stayed with a 265/65/18 so I can hope to limp out if it all goes wrong. But if you really want an MT, there might be a much better option - GO fit some 17's. You can get good MT's in <32" in 17's. To get 17's to fit you will need front caliper carriers and rotors from a v6 (which are available in the US). Then get someone to send you over some 17" wheels from europe (no 17" were sold in the US) and you're off an running
One last thing, you're not required to stay with the airbag system. Atlantic British just released a conversion kit last month. No real info on the website but it was in their catalog. Around 1k depending on shock option. Although I don't think anyone has installed it yet.
