You seem to have 2 concerns:
1) taking away business from the company. Chofetz Chaim would tear up a post office stamp whenever he would send a letter with someone travelling to the same destination. So, this is definitely a valid concern but also a hiddur. Furthermore, in his case, this is an ongoing and self-initiated problem – if a lot of people will stop using mail, the losses will disrupt the service. In your case, it is a once-a-year thing and they made the rules.
2) appearing to be scheming. How about you just tell them your plans and ask their opinion? Only you had to ask an owner, not an employee who does not care. Maybe suggest a small extra fee to make it agreeable.
actually 3) doing business with non-Jews around their holidays. If nobody comes, and here is their regular Jewish customer who helps fill the season, will they praise whoever for that?