Instead of moving the bass clef to the left by itself, you could move the other clefs to the right. In Library > Music Symbols, search for G clef, delete the existing glyph and add the glyphs staff1Line (U+E010) and gClef (U+E050). Select the first glyph, reduce the Y scale to obtain the desired horizontal displacement of the clef and change the Y offset to move the staff line glyph over the X axis. Then do the same for the C clef.
In the following example, the Bravura G clef is moved to the right by setting the Y scale of the staff line glyph to 30. Note how this glyph is hidden inside the G staff line:
You can now move all of the clefs to the left by reducing the spacing gap before clefs in the engraving options.