That won't change the fact that your business name will still show the same on both sites.

Nevertheless, as a response to PayPal's reply to you ...

1. You can do the same thing by creating separate Page Styles in your PayPal profile, and specifying the appropriate profile name in your store PayPal module settings.

or

2. You can simply uncomment the appropriate line in your /includes/languages/english/modules/payment/paypalwpp.php file ... and it'll automatically pass the appropriate parameters.
Code:
////////////////////////////////////////
// Styling of the PayPal Payment Page. Uncomment to customize.  Otherwise, simply create a Custom Page Style at PayPal and mark it as Primary or name it in your Zen Cart PayPal WPP settings.
  //define('MODULE_PAYMENT_PAYPALWPP_HEADER_IMAGE', '');  // this should be an HTTPS URL to the image file
  //define('MODULE_PAYMENT_PAYPALWPP_PAGECOLOR', '');  // 6-digit hex value
  //define('MODULE_PAYMENT_PAYPALWPP_HEADER_BORDER_COLOR', '');  // 6-digit hex value
  //define('MODULE_PAYMENT_PAYPALWPP_HEADER_BACK_COLOR', ''); // 6-digit hex value
////////////////////////////////////////
I strongly recommend option #1 ahead of #2, because it doesn't require any code changes, and lets you change the style on-the-fly.