Tb--that accumulation of creosote is an indication that your flame is not too hot---that's good. a cool smoke is much better for the bees than a hot smoke.
I don't know exactly how your smoker is constructed, but mine has a seam around the lid. I fit the tip of the blade of my hive tool into the seam and, using the bellows as a fulcrum, pry up the top quite easily.
After a certain thickness of the creosote accumulates, it usually gets brittle and can be "crack-pealed" from the inner surface of the smoker (using the hive tool).
But yes, it definitely is a nuissance.
A new trick I started using about half a year ago was to take chunks of the residue left behind after I melt out the wax from my old frames in my solar extractor. Unil recently, I used to just throw it away. The residue contains wax, propolis and exuviae and burns nicely, for a long time, and, from my esperience, seems to help calm the bees. I don't use only the residue but add it into the smoker to burn together with my other fuels.