getting Engine up to 40C temp??

Just had my beloved 1996 V8i converted to LPG. The engine needs to get to 40 degrees before it will change over to LPG, and on mind it seems to take an age (From cold), which means I'm wasting money on petrol!!!! How long should it take to get to 40 degrees, is there anyway of speeding the proccess up
Thanks

get the conversion changed so it flicks over at a certain revs above idle. when the efis start the revs go up for a few seconds then drop back down. mine used to change over as soon as the revs started to drop off. the signal is picked up off the red wire on the throttle potentiometer on the end of the throttle body butterfly.
never had any probs with mine even in the cold weather.

my 2000 d2 changes over after about 1/2 mile in summer and maybe 1 mile in winter so fairly quickly. what do you call ages?
do you wait on idle for it to change? I just get in and drive which warms it up quicker