Yes, you can... but its a complete waste... 500mg is already FAR much more than the daily needs (833%, or more than 8x). Ive heard the body can absorb at most 500-1000mg/day, so if you ingest more than it, it will be simply expelled unused.
For me, the C vitamin seems make me less sleepy and more alert during the high. I never tried to measure the duration of the high... but im planning to do it today and see what happens.