Took time for me to get this since I didn't know what a score buffer was so this is to help anyone who finds his/herself in similar situation.
All you need to do is go for your pick-ups (yellow things) in a row and fast so they don't get added to your main score. You need to collect them quickly and that'll maintain a buffer (the time it takes for a score to be added to your main big score), now collecting 100 whilst maintaining the buffer will earn you this achievement.
I did this on a track 8 variant on Normal since it has lots of boosters and your ship is faster.
Tip here is keep an eye on your main big score, make sure its 00000 and make sure the score under it keeps moving whilst collecting your pick-up. Don't crash!! Try to get a 1000 score or more and that's it.
Hope it helps.