Yes, the only way now is for your buyer to make a seperate payment for the balance, via Paypal, check, cash whatever.

Next time, add a shipping calculator to your listing or indicate a flat fee for a single method of shipping.
It is also a good idea to add one of two dollars as a handling fee to the estimated shipping cost as the actual postage or freight charge often ends up being a little more than expected + it covers your packing costs / label printing etc and is an acceptable practice.