I've used this trick from time to time:
Play two sixteenth-notes and then a sixteenth-note triplet, that adds up to one beat. Loop that, and then start "evening" the notes out, until you have a steady flow going, all the while tapping the beats with your foot. Or leave a metronome on. But that's my advice. Use the closest possible rythmic figure, and then try to smooth it out so that all the notes are the same length.