Yes those windy days can be a pain. The best I can offer is to add to your "tools of the trade" a block that you can put under your oil pan to raise it up higger so that the oil has less distance to drain. The lesser the distance the lesser the blow effect. You may want to also carry a few various sizes of cardboard that can be folded and stood up to place (wedge in) under the vehicle to help block the wind. Mobile oil change is a great business but you do have to be creative sometimes to deal with weather issues.
Hang in there!