To expand on what Katank said, it's very easy to 'distract' an infantry unit with HAs. I've had great success with this. You don't even have to micro them. Have the HA flank their army, and close on the BI position, and open fire. Most likely, the BI will attempt to give chase. As long as no cav chases your HA, just leave them on skirmish and forget about them. They aren't likely to do a lot of damage that way (I usually get about 30 kills), but the BI will be effectively out of the battle, for only the price of a couple HAs. This gives you plenty of time to take out the rest of the Byzantine army, and should leave you enough troops to deal with the BI once your HA run out of arrows.

Bh