How about a timed-stickybomb/missile? Hear me out first;
Have this bomb/missile target an opponent and hit them, but not explode. Instead, have it stay on them and after maybe 5 seconds or so the explosion goes off. But to add a more interesting dynamic, have the bomb be tradeable.
Let's say you've been hit with this sticky bomb but you have a racer in front of you. The count-down starts and you have less than five seconds before you're blown to Kingdom come. If you're fast enough to catch the guy in front of you, you can bump/ass-ram/slam into him and the bomb gets traded to him. Let there be a 1 second non-tradeable time frame before it can be placed back to you, but still have a small window of opportunity for the opponent to give it back to you. Once the bomb goes off, have it only affect the victim unfortunate enough to endure the final moments of the count-down.
This can be high risk version of tag or hot-potato while the race is going on. I've noticed that slamming into the other racers doesn't really do too much for racing dynamics, so this can add a more aggressive playstyle to the game. We're already trying to mess each other up with all the power-ups we get during a race, so adding something like this can really stir things up!
---I realize all the balancing issues can be troublesome the more items you put into the game, but this is just something i kind made up on the fly. Feel free to take parts of my idea, the whole idea, or only one aspect of my idea as you please!