I'm sorry, but you probably could not. The male betta would almost definately attack and kill the guppies since he'd mistake them for another male betta due to their colors and finnage.
I wouldn't suggest it since so many females are agressive, sometimes even moreso than the males; after all, male and female bettas can't go in together, so if the female thinks the guppy is a male betta, she'll probably fight.
Or, she might even think the guppies are other females, and since it'd be two guppies, there'd be three "bettas," which might make the betta girl want to fight the two guppies for dominance as its not the magic # 5. Did that sentence make any sense?