You can add a few shrimps in there, maybe Red Cherry Shrimps or a amano or two at most. These are pretty much the hardiest shrimps around, so they're more forgiving than most.
However, its always best to have the tank running for a few months least before adding shrimps, to ensure tank is established a little bit.
As a side note, guppies do better in groups of 3 at least, spreads aggression, so I'd add one more guppy.