Question is in the title. I'm using VirtueMart 1.1.8.
Log in to your account > Profile > Website Payments Preferences > PayPal Account Optional: On
Note: This only applies you use the Website Payments Standard integration. For Express Checkout (in VirtueMart called "ppapi"), you'll need to doublecheck whether VirtueMart supports sending the SOLUTIONTYPE=Sole parameter.