Quite a few people just use an extension, particularly on the larger scale traction engines when raising steam. Use it from the start as you would a blower, you can even light a bit of soaked rag in the smokebox to get some hot gasses going up the chimney to start it drawing.
Remove once there is enough pressure to use the steam blower or leave in place to keep the smoke out of your face when driving.
I have also seen extensions with a pipe comming in at the side at an angle pointing upwards which can be plumbed to an external blower with some flexi hose.
J