I don't believe you'll find a specific tune for an underseat K&N; but, I don't believe there'd be much difference, if any, with an undertank K&N. The underseat K&N has been on my tadu list.
On the otherhand, leaving the fresh air duct in place under the seat may be an air flow limiting factor that will negate any improvements with the K&N. I removed the air duct for other reasons.