No good way to switch. I use bbf full time now. The U's as mentioned above will work. I have one set for shutter button. I don't use it for myself, only if I hand the camera to someone to take a picture. The U settings make me crazy though, I can't remember exactly what they are set for. And if you tweak some settings, they are not saved unless you save them. So that added to the confusion.
Now for bbf, you love it or you hate it. It took me a year to decide I really liked it and get used to it. I found it was NOT good for me to switch back and forth. I have the opposite problem as BF Hammer. When going back to shutter, I can't stop myself from hitting the back button and nothing happens. I shoot birds and bugs and bbf with a single point and bbf. I find it to give me the exact focus I wanted. I often describe it as power assisted manual focus. I can focus on whatever spot I want with perfect precision. If the subject is moving, I just hold the button down and follow it. If it is stationary, I focus on the subject and release the button if I want to recompose.
I do sometimes switch to a multi point mode for small birds in flight but I still use bbf. Just more points.