This is something I've been working on as part of my commitment to get more odd groupings into my playing. I wrote about doing this in 4/4. It's in The Jan. 2010 and March 2010 issues of Percussive Notes and can be ordered here. (BTW, I have an article on crossovers in the current issue.) Although we're dealing with waltz time, the concept is the same. Take rhythms you're familiar with in 3/4 that are 5 notes long (a quarter note triplet and two 8th notes, for example) and after you've played that for awhile, start working towards slightly slowing down the 8th notes and speeding up the triplets until you have 5 equidistant notes in the bar. Now I had one fellow who worked with me who preferred to figure out where each note of the quintuplet worked out in 16th notes in the bar, and probably for some folks, it's a good method. I found for myself however, if it got too "mathy" it was hard for me to access and I also didn't think subdividing 16ths helped the feel too much if it was a swing setting. The same individual tried to tell some folks later and out of my presence (I know, classy huh?) that my way of doing this was baloney and I was just guessing at the grouping. Nothing could be further from the truth. As drummers, we're always working on ideas that are based on equidistant beats in the bar (Quarter notes in 4/4 time anyone?) so all I've done is worked on hearing this with 5 and 7 note groupings to find the groove in them and be able to play them as naturally as possible.
Here's me first counting in 3 and playing 5, then counting 5 and playing 3, then I repeat the whole process with 7.
Now I sing "Someday My Prince will Come" while tapping out 5 and then 7. Hollywood is going to be calling. I can feel it!
Finally, here I'm trading 4 bar phrases in 3/4 using only 5s and 7s in the trades. (Near the end I'm leaving more rests for extra wackiness!)
I have also sometimes doubled and tripled the odd groupings, BTW.
So... you may not use this stuff tonight, next week, or next year even. But I have found all this stuff has improved my time immensely. If you can divide 3 into 7 equal parts, dividing it into 3 is like a vacation!