Jim Elbrecht wrote:

I've used the pipecleaner-in-the-tube trick with varying results.

I recently tried to use a can for a second time. I found that it was
relatively easy to push the dried crud out of the plastic dispensing
tube using a wire. It was the short shaft sticking out the can where
the problem is. I used a drill bit turned by hand to dig into that
shaft and pull out more crud, some of it semi-solid.

I eventually got it to the point where there was a constant small air
leak coming out of the can. I put the dispensing tube back on, turned
the can upside down, and a very weak but constant flow of foam began to
flow. I thing it would only flow if the can was upside down. I stuck
the nozzle where I needed it, rigged the can so it would stay put (and
stay upside down) and left it. I'll check today to see how much came
out.