Driving tracks backwards

So far, in tts, I have managed to drive most of the tracks backwards. The only ones I couldn't were:
SNES Mario Circuit 2
GBA Boo Lake
GBA Cheese Land
DS Figure-8 Circuit
DS Luigi's Mansion
DS Waluigi Pinball
DS Mario Circuit
DS Airship Fortress
DS Bowser's castle
DS Rainbow road

There are also some which are only feasible via... questionable methods. This usually means some sort of ultra shortcut, which I don't know if it would be possible otherwise. For reference, when I say "the start" or "the end" of a track, I mean when you are driving it normally, not when you are driving it backwards.

DS Wario Stadium: I found no way to get past the canon near the start, so I had to resort to abusing one of the jumps near the end to jump out of bounds to just go straight to the start.

DS DK Pass: I wasn't able to get past the canon near the end, but by shrooming I could get enough air to make it to the tunnel, which just allowed me to skip most of the track. Once, I managed to make it across, but I hit the canon and was just sent straight back. It might be possible to complete it without the ultra but I couldn't.

GBA Ribbon Road: This one was easier and less egregious. The first barrier I easily passed by using the ramp in the middle of the road. But the second one was harder. I found that by going past the first barrier, and then going sideways and using the ramp I could manage to get a respawn that got me past it.

GBA Lakeside Park:to get past the first barrier, I went sideways, following the wall, which allowed me to get past it. However, I later realized by abusing the ramp that sends you to the middle of the track, I could skip as much of the track as I wanted. I wasn't sure where the limit was for this. This track is absolutely completeable without the ultra, but the problem is how much are we allowed to skip?

For most barriers (ex. small jumps in SNES Bowser's Castles) I could just hop over them, or use a shroom if necesary. Often the game was very gracious with respawns as well. Some tracks seemed very close to being completeable, with just one thing in the way.

GBA Boo Lake: You can make it past the first big jump by simply jumping into the void. However, the second one, no matter how close I got, would never give me the respawn, and though I was able to get quite close to hitting it by using 200cc and the boost panels, I never managed to get there.

DS Bowser's Castle: This was SO close. The ending canon can be bypassed by jumping into the void for some reason, I don't know why it respawns you so far but I'll take it. Then we hit the obstacle I couldn't pass, the rolling metal bar. I tried my best, but I couldn't get past it. However, I went the other way around to see if there were any other obstacles. I found out that there is just like...no wall to the side of the little space before the bar? I don't know why this is, or why I can just drive out of bounds, but you can pretty much just make a straight shot for the first room, and then there aren't any more obstacles. If anyone finds a way to make this work PLEASE tell me.

Now here is pretty much the ONE track that was decently hard:
GBA bowser's castle IV. On this track it's all smooth sailing until you reach this one jump across. There is lava before you and walls after that. However, I found out that to the left there is a small gap into more lava. I found that if you jump and manage to get into that gap it will respawn you before the jump, and the rest is easy.

Tell me your thoughts! Also thanks for reading all my rambling