Clenching, breathsmoking, whatever technique you want to call it... it's all really as simple as just keeping the pipe in your clench, while smoking it as little as possible... really, just having it in your mouth without consciously doing anything with it is the best way. The key is just not overthinking it.
Your natural cadence with your breath, will expand the gullet of your throat, keeping a constant in and out of air, and will be just enough to keep it lit.
No, you don't blow smoke out at all. Really your best smokes are always going to be without any evidence that your smoking at all, so no one will ever really see me blow smoke. That's more of a cigar thing anyways.
I have accidentally walked into grocery stores, malls, and even the art museum while smoking my pipe. I just forget its there. And, I was all the way back to the contemporary art section when I realized I was smoking. No one said anything to me, mostly because you can't tell whether I am just walking around with an unlit pipe or smoking.
Big billows of smoke are more reserved for folks that just started. YMMV