Yeah.... hang an electic motor on your frame rail where it's a prime target for rain/snow/road salt etc... No thanks.

...and on to the original question. I'll go out on a limb here and "assume" that you know what you're working on. You've stated you have no voltage to the "in tank lift pump". That would mean it's had the retrofit kit installed that mopar came up with for an in tank installation. As noted....your truck was born with a lift pump located on the engine right behind the fuel filter canister. This would mean that you have had a relay and small wiring harness installed as part of this upgrade. There is an inline fuse for this pump..... is it ok? There is also a relay that is energized by the "original" lift pump 2 pin plug that attaches to the add on harness. I'd be doing a voltage test at that connector. It's simply a B+ directly from the ECM and a ground. If no voltage there, yes, it's possible the driver in the ecm has failed. If that's the case I'd do exactly what you mentioned..... find a key on B+ source and use that to energize your relay.