Thankfully, you don't have to do this on Guitar, even though the description really doesn't say you have to anyway. The easiest way for you to do this is on Hard Bass. On Hard Bass, the chart is slow and there are no more than two hammer-on/pull-off notes at a time.
If you are having trouble, there's not a whole lot to say than practice. If you think that you're playing perfectly, then check your equipment and calibration settings to see if they're off. Otherwise, practice. Also remember, you don't have to play well, just hit all hammer-on/pull-offs.
The guide would like to thank forum user Darth Trom for making this technique known.