I have heard of this but have not tried it..  Get about a yard of extra fuel line.  Put a t fitting between the fuel pump and carb and run the yard of fuel line up a stick, I would suggest a yard stick with the line taped to the scale.  The line should be open at the top.  The presure as supplied should be about 1/4 PSI which is less than a foot of fuel head, or about the same as muffler pressure.  It should not go over the top, however I suppose it could, especialy right at startup before the regulator has a chance to react.  If I were to do this I would plug the top of the line, then unplug it after the engine starts, ready to plug it back right away.  In fact I would probably use my hemostat.