Probably the only way is to use the block in the (EDC) script pic costumes library, although you would have to figure out how to get rid of the block background.
Also, how did you turn the symbols to SVG? I might be able to take some of those precious SVG paths for my own projects... (crediting you for the sourcing)
I went to the snap source code and basically just converted the canvas drawing commands to svg path commands (although some I could replicate with just regular svg elements, rather than a path, for example, $square can just be done using a <rect> element). You can view all the snapblocks icons here.
Yeah, I know the symbols are drawn using a canvas. I'm started thinking of a "Bad Editor" idea where it's Bad Apple ran in the editor with the help of one tiny big symbol, but this is unrelated to my question.
You could use XML editing to make a transparent block and use Flat design to remove the shadow.
Edit: I just realized that transparent categories don't work in Flat design, so set Fade blocks to 100.
Edit 2: That just makes it have a white background. I don't think it's possible to automate without keeping some junk pixels.