This is definitely possible!
First, remove the brake pads.
Spray brake cleaner around the piston and the dust seal.
If needed, use an old toothbrush or a soft brush to loosen any dirt.
Wipe everything clean with a cloth.
Then carefully pump the piston slightly outward by gently squeezing the brake lever (do not pull the lever all the way).
Finally, try to push the piston back in using a plastic tire lever or a piston tool.