Heat is the only thing I know of. I just had some new asphalt installed and when the guys showed up, it was very hot. Like 300° or so. As it cooled, it become harder to work with. Where they put it over cooler or cold asphalt, they warmed the old stuff with a propane rose bud torch.
I don't know how to tell you to warm it though, you probably don't want it in your oven.