Check, if if really uses the title tag - if so, you can append the title tag with an action as described in the FAQs
/t/967/1
the format string would look like this:
$num(%track%,2) - %title%.
It could also be that your car stereo uses the filename. If you want to rename the files then use the (menu) converter tag-filename and a mask that looks like this:
%album% _ $num(%track%,2) _ %title%
This would then create filenames that group the tracks by album and then by track - pretty much like the CD it came from.
BTW: what does the filename now look like?
Actually: if your stereo really uses the title as sort criterion then you would also have to refill the title tags as with only a leading tracknumber you would get all the files with a leading one, then all those with a leading 2 and so on - but probably you want to have them album by album.
As your car stereo apparentyl follows very specific rules I would always create a separate set of copied files to be used on that device and keep the other library as it is.