I feel your pain. If I had six week old chicks inside I'd probably be divorced.
What does the coop look like? Does it have good ventilation but also good breeze protection where they would be? If so they could probably go outside now. I've had chicks younger than that go through temperatures in the mid 20's. If you can take them outside early in the morning when it is that cold and see how they react. You may be surprised at how well they handle it. I understand your desire to acclimate them, I raise mine in the coop so they are acclimated. That may be one reason mine can handle colder temperatures younger but yours may be old enough without that.
If you have electricity out there you can provide heat, whether a heating pad, heat plate, heat lamp, incandescent light, or an emitter. With any of them be careful with electricity. That may be more for your benefit than theirs though, they probably won't need it. Once they are feathered out they can handle cold much better than many people think. Most chicks are feathered out at 4 to 5 weeks.