Practice quintuplets, septuplets etc. by using Konnakol. Set your metronome to an easy tempo (you might go as low as 40 bpm), clap your hands and use the appropriate syllables. Choose the continuous syllable variations rather than the variations that leave out notes in between.
When you feel comfortable with the previous exercise, practice the rhythm units on the tuplets, one by one. Begin with the busier units, as they are easier to execute.
When you feel comfortable with every rhythm unit, move through all the rhythm units, switching every bar.
If you want to go even further, try applying the grouping exercises or cross rhythms to tuplets.