Is the Seneca the only machine on the cert?
What worked for a company I once worked for was knocking on the office doors downtown with a brochure and asking if they thought about what chartering could do for them. He had 2 Navajos. This was in the midwest and within 2 hours of large business centers at CGX,TEB,CPS,ATL etc. Plant the seed that they can go from their closest airport SUA/FXE/PBI to TLH/CRG and back in one day, 2 or 3 people, no TSA, no body cavity searches. Most business people react positively to things that make their lives easier.
Consider offering 1 or .5 hour free to first time customers with the purchase of at least 1 hour.
Give away 2 hours as a prize in some kind of fund raiser/raffle. This usually gets you loads of free advertising by the sponsor.
All the best.