Probably not - the code for powerups doesn't leave many loopholes. to set powerup state on a player, the code requires an entity with the classname of the actual powerup to touch that player. Only thing I could possibly see working is some kind of trick that teleports a powerup onto the player every 30 seconds, but not clear how to hit that moving target.

As an alternative, consider repeatedly respawning the powerup (using a simple hack), so the player can have the effect continuously, if only they go to pick it up every time. 

Ah-well, thanks anyway Preach. Back to the drawing board!