I assume we aren't talking about a '72 motor here.
You cannot use a non-pulsed source to hold them open - or least not if you don't want to burn them up.
Someone can correct me here, but I think in operation, the injector is opened initially by a greater current then what is used to keep it open. In other words, even using a pulsed 12v source might not be sufficiently safe.
-Chris