Not that I practice what I preach but you may want to try ...
Method one:
Stiffen your right hand and keep it slightly (but not painfully) rigid through the motion of playing the artificial harmonic with your thumb pick. Remember that your hand is actually moving in an arc away from your body as you pick. Practice by playing the harmonics - both as arpeggios & full chord strums - chromatically one fret at a time always keeping your right hand 12 frets away from your bar hand ... bar on 1st fret/right hand on 13th, bar on 2nd fret/right hand on 14th, etc.
Method 2: For single note runs you can try using an extended finger or curl the finger under your right hand palm. Jerry Byrd offers the advice of not psyching yourself out about harmonics ... to just play them naturally like any other musical passage. There's some merit in that. the more I think about it the more I tend to miss them but you have to put in the slow tedious practice to get there. [This message was edited by Andy Volk on 03 April 2004 at 12:33 PM.]