I think the best you can do ... is fake it. Like usual
Have the "train" part of the tram run into a depot at the edge of town, and start the "tram" part of the route there from a tram depot. Using precise time schedules, it might look like one vehicle. Kind of. ^^
I already tried a lot of times this kind of thing, like with precise time schedules a bus going from a big city to a smaller city with a dock, then the passengers are transfered to the dock and just after the boat comes and take the passengers to an island.
I also tried, by destroying tons of buildings, to create a "downtown railway line" which follows roads. It allows for my intercity trains accomplishing a long travel to start downtown to get more passengers
I've also read "NotRoadTypes" and it looks pretty cool.