It would require writing custom code for the specific requirements you have.
Some things you'll need to consider:
a) what if customers order a combination of products, with your 'unique' product being only one of several in the cart ... how do you handle that case?
b) you'd need to find a way to recalculate "just" that product's shipping, taxes, discounts, etc, in addition to any other products in the cart
c) you'd need to find a way to supply credentials for the "other" authnet account in order to send the charges in the right direction
etc
.
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