Hi,
The best would be to upgrade to HikaMarket Multivendor. With it, you can restrict different payment methods for different vendors, and thus you can assign a payment method for one vendor and another for the main vendor. Just change the email address (or other credentials based on which payment plugin you're using) between the payment methods, and have them use the same payment plugin.
Then, in your product for which you want to be linked to the other PayPal account, select the vendor you created for the payment method linked to that PayPal account.
Without HikaMarket Multivendor, you could use a trick like having a weight in that product and not in the other products, and have no dimensions for that product, and dimensions in the other products. And then, you can use the weight and volume restrictions in your payment methods to do something similar. However, with this, you're limiting yourself to only one other PayPal account (with HikaMarket Multivendor, you can potentially have many vendors, each one with its own PayPal account linked), and you can't use shipping methods which rely on the weight and dimensions of the products to calculate the shipping fee like UPS, USPS, Fedex, etc.
