I'm not sure about using a virtual Visa or Mastercard to buy a Target GC. You can only use a Target GC to buy a Disney GC in the store; you can't make the purchase online.
Idk but another method might be: can you cut Target out and use the virtual Visa or MasterCard to buy a Disney gift card straight from the Disney Store website? I see they have free shipping on gift cards.
ETA: make sure to read the terms and conditions of your virtual visa fully. I got some type of virtual visa from doing a Hyundai test drive last year for $50 and in the terms and conditions it was limited to 1 time use- if I didn't use it all at once the balance was forfeited!