it seems like an insurance company would make an "event policy"
where you only use it for that certain amount of time, then it cancels.
I've done it a couple of times with my commercial limousine policy where I needed a non-employee driver to transport some guests, for 1 trip/day.
I have heard of others on here buying higher insurance for 6 months, delivering the bus, then dropping the insurance... But, I haven't tried it personally.
I mean heck, they've even got Hole In One Golf Insurance!