You should still be able to manage Cory. I haven't yet got a pressure regulator on my compressor, so I'm in the same boat. You can practice on something first, just trying to mist on the mottle, building it up, using a slightly lighter shade of colour than the required finished shade. If you have problems with it 'splattering', or similar, try uising a hand-held card mask. Cut a few iregular small holes in a piece of thin, but stiff card, spacing them well apart. Hold the card varying distances from the surface to be painted, and spray through the mask. You should get different effects of mottle, and feathering. Worth a try if you can't go straight to the surface to be painted.