The answer, eventually worked out as follows:

Asked several locals, got lots of blank looks.
Googled, checked lonely planet, didn't get much.

Taxi driver who had quoted me US$40-$100 when he dropped me off at the hotel turned up at 6.15am and banged on the door for two hours, despite me never agreeing to it, so I figured that was a good sign it was overpriced and he was getting good money :)

I went to the NE suburb taxi rank, and asked there.  Again I was surrounded by 'vultures' before getting out the car, but I played them against each other, and there was a car leaving in 5 minutes for about US$24 or so.  It wasn't 4WD, but the locals were all in it so I figured it must be ok - most of the cars weren't 4WD.

On the road, I sorta wished I wasn't in a Nissan Maxima, the bumping and jolting was insane. But the story of it, the spectacular views on the two 3500m+ views and the two 'tunnels of terror' (flooded tunnels you drive through!) made it worthwhile, and we got in after 7 hours.  Love random travel like that!

Khojand to Dushanbe - cost vs danger?
I know this is a rather controversial issue. I was skeptical as well before doing this on my car, and I have not refilled my car tires for several months. Before that I needed to adjust the pressure every couple of months at least. 

Now I think it is a good idea to try this for our bikes. Especially since, when I see I need to fill up my bike tires, I get too lazy and give up the ride altogether. 

Is there a way to do this at home?

EDIT:
I thought I'd update the question for people who come and read later:  

Thanks for all the comments, I drive a lot (30kmiles/year) and I saw (to my surprise) a significant difference with nitrogen. 

I understand the reasoning with losing oxygen over time and increasing the N2 concentration but in practice that does not happen fast enough.  

I think I'll look into Helium/Argon and I'll update you if I managed to do something interesting. 

And I live in a small place I don't like to have a large pump but that is exactly why pumping is such a chore for me,
