Could you filter it? I've read that filtering can remove some of the hop flavor, so maybe it would help reduce the spice flavor.
Probably not enough, but maybe.
Also, what about adding gelatin to fine it? Would this help pull any spices out of suspension?
My guess is neither of these would have a great enough impact. But they might be worth trying, particularly with the minimal cost of gelatin.
If you brew a batch for blending, you could always blend it in a pitcher at serving time. That way, you wouldn't necessarily wind up with 10 gallons of over-spiced beer.
I've actually been thinking I should've brewed 10 gallons of pumpkin this year... Mine came out underspiced, so I soaked spices in alcohol and gave it a tweak. Now it's just right.