I was thinking about that too Ace, but seems like a heck of a bunch of work.
I was also thinking of a script which gets the highest altitude of a vehicle. Like if you setvelocity [0,0,100] to a bicyckle and to a jeep, the bicyckle will naturally go higher, thus it being lighter than the jeep.
To take this further, if we know the mass of the bicyckle and it's hight in relation to the jeep for example we could count the jeeps mass with a script.
But what you're telling me is that there's no
_massLST = getmass LST ;D :'( ;D