If it is white smoke then the issue is that there is to much unburnt-fuel. This could be old dirty injectors or the pump timing could be out, or low compression.
My guess is both since it is worse when its cold that is more likely to be timing. But the injectors get lazy and sort of dribble when old and dirty.
The few easy things I would do is get Diesel purge and feed it directly to the fuel pump to clean it out. If you do not want to remove the lines and clean it that way I would get "Power service Diesel Kleen" silver bottle and run it at 2-3 times the standard dose. I personally add 6-8oz or Diesel kleen and Synthetic two stroke oil to my diesel (its a 02 TDI golf 15.5gal tank) at a 40-60 mix. At the very least i would recommend running two stroke oil on any older diesel since they were built for low sulfur fuel and not Ultra low sulfur fuel that has less lubrication see
http://www.dieselplace.com/forum/76-speciality-forums/64-maintenance-fluids/177728-lubricity-additive-study-results.html
Someone could also try spraying a fine mist into the intake when the engine is hot and running. That will steam clean the cylinders but the down side is if the rings are worn and the carbon in the cylindar is keeping things tight that could be cleaned away and reduce the compression.
There is a Trusted mechanic for VW TDIs at "Celtic Motors, Kalispell, Mt 59901" it is about 2hrs away but they might beable to help or point you to some one in the area.