on the day of the bp test, when they are checking your bp, bair down like your taking a shit. Like if you were constapated and were trying to push it out. push pretty hard (but try not to actually shit yourself) and that will drop your bp very quickly.
Another option is to take a pain killer before the bp test seeing as how pain killers are known to lowere bp. That is of course if there not testing for that kinda stuff the same day or whatever. Go to Wal-Mart and use that bp machine thing near the pharm and practice the bairing down thing if you want to get it down perfect and know just how long you need to do it beforehand. Good luck.