Those are actually the easy ones to "fix". Either disassemble and pull the spring out, or if it's the push then twist version, just force/ twist the spout past the plastic nub that's supposed to limit how far it twists.

Either will allow you to hold the valve open without force.

Of course a properly sized/ shaped funnel without any spout at all is even easier. Which is basically how the metal safety cans work. Also helps to drill a vent hole on the handle, and use a sheet metal screw as a plug.