I think it depends on the kryptonite involved, if we're talking about Earth-One's universe. Green K's effects were temporary and wore off if there was either a protective lead barrier or it was removed from close proximity to the affected Kryptonian. Red K's effects were isomorphic and wore off after a specific period. Gold K's effects were permanent. Jewel K acted as a telepathic transmitter for Phantom Zone criminals and was only featured in a single story, so it's difficult to draw any inferences about its proximity effects. It's been established that lead blocks kryptonite radiation, though, so it's possible that Hal (or John, or other Green Lantern Corps members) could create a lead barrier construct with their power rings rather than use the beam settings exclusively.

In Earth-Two's universe, the effects of kryptonite-two were temporary and proximity related. I imagine that all Alan needed to do was find a suitably dense lead pallet to protect Kal-L and Kara from radiation poisoning with his power ring, or simply rig up a power-ringed pair of clamps or a catapault to get it out of harm's way.