If the entire song were in 3/2, 3/4, 5/8 or whatever your unconventional time signature is, it'd be as simple as counting the steps and putting in an H command where appropriate. (Step $8 of every *other* phrase; step $C of every phrase; or step $A of every phrase, for the signatures I mentioned above.)
But that song is in 4/4, with a weird bassline, if anything. So, in order to have different channels/phrases in different time signatures and still have them meet at the first beat of the phrase that follows, you'd have to go down to your groove screen, calculate the amount of ticks in your 4/4 phrase, divide that by the amount of beats you WOULD have in your new time signature, like, say 3; and then use the D command in a particular phrase to program in the triplet.
Otherwise, you could make a new groove for the entire phrase where you still have the same amount of ticks, but your notes are spaced out differently so that they end up as a triplet. Just remember to come back to your default groove at the beginning of the next 4/4 phrase for that channel.
There are threads about it that explain it better than I do, and with more detailed examples, but one way or another you have to math.
Good luck