You might be able to stretch yourself out with a series of dildos. Start with one that's just a bit of a stretch, and use it to masturbate. You could probably even insert one and then watch tv or something and relax. When you get to the point where that one is no longer so much of a stretch, go up a bit in size. I'm not sure how long it will take, but you can probably loosen yourself up a bit.
The other thing is that if it's not too tight once you get going, you don't need any stretching. I always need a few seconds after getting it in for my body to adjust, and it can take a few tries to get in in the first place. Once my body has adjusted, it's fine. So if that's how you are, all you need is to go slowly at first and then go up to whatever speed you'd like.
Just take your time. There is no rushing it.