Betablockers are for those who want a quick emergency fix (not judging, they have been good help to me as well). A 20-50 minute aerobic workout has the same net effect for many (healthily burning adrenaline instead of using high blood pressure medication to reduce anxiety).
but working out before something like a speech where you can be nervous and have an elevated body temp is a bad idea because you will be much more prone to sweating. i've experienced this and it is terrible.
Be sure to check Dr. Medina's brain rules for presenters: http://www.slideshare.net/garr/brain-rules-for-presenters