There are situations off a scramble or near stalemate where you can pull off a sweep and there are other situations that it may work. The problem is if you get caught you will be behind very quickly if not pinned all together.
Usually the guys that can pull off sweep like moves are already good wrestlers. You cannot hope to just have a pull guard and sweep game in HS wrestling. You will have to be adept on your feet and from the refs position, both top and bottom.
Leg riding will be natural for you if you can figure out the single grapevine but double grapes (i.e back mount) is something you will already be comfortable with.
I will see if I can find a vid of a college wrestler with a funky style that basically pulls off a sweep.
***EDIT***
Here is a vid:
157 Matt Cathell vs Trent Weatherman | Iowa St. vs Kent St. on Flowrestling Check 1:22 of this vid and this is against a wrestler from Iowa state, one of the top programs in the Country. Its not so much a sweep but he almost gets one during the exchange, but it is basically a half guard pull and back take for 2 points.
I also created a whole thread about this kid since he was so fun to watch.
http://www.sherdog.net/forums/f12/funky-kent-state-kid-1420635/