I used to do it with a soft (ish) case, it wasn't too clumbsy, but it did push up on me a bit, I had a a case that allowed me to carry it like a backpack (rucksack, however you call it)
Only problem with that is that it feel like you are dragging a parachute, another thing I did is tie the two tightening straps together at my stomach, as the first time I rode off, the air resistance pulled on the guitar hard enough to loosen the straps holding it to my back. It won't be bery comfortable and any sort of speed, but it's doable, I've gone about 10-15 miles hitting around 60-80mph whilst ferrying my guitar.