Hi there, Kayci!
Based on the procedures from the Walt Disney Travel Company, it sounds like you will be able to pay the balance in full via check sent overnight (I have emphasized the relevant material):
"PAYMENT PROCEDURES:
A DEPOSIT of $200.00 per reservation is due within 10 days from the date of booking. **IF THE RESERVATION INCLUDES THE PRICE OF ANY PROMOTIONAL OR PUBLISHED AIRFARES, the $200.00 deposit plus full payment of airfare must be received at time of booking or the reservation will be automatically canceled.
FINAL PAYMENT is due in our office 21 days prior to guest arrival. For all packages that include airfare, final payment is due 45 days prior to guest arrival. 'Land Only' bookings made 21 days or less prior to arrival must be paid in full at the time of booking. FINAL PAYMENT can be sent to Walt Disney Travel Co., Inc., P.O. Box 10375, Lake Buena Vista, FL 32830. For overnight delivery via private courier service only, send to: Walt Disney Travel Co., Inc., 7100 Municipal Drive, Orlando, FL 32819. Please note: regular US mail service does not deliver to the Municipal Drive address. Vouchers are proof of final payment."
For any payment, modification, or cancellation questions, it is also possible to reach the Disney Reservation Center by phone. The number to call is: 407-828-8101. While you'll certainly need to let them know how you intend to pay for your trip - via check - you might also want to give a call when it's sent to provide them with a tracking number,
Have a wonderful trip!
See you later, celebrator,
-Deborah B.