It's entirely possible that self-administering anal stimulation may help you know how it will feel for him, even though each person's experience differs. However, providing anal sexual actions to yourself and to another person are quite different things, in terms of position, where you can reach and what you can do.
If you don't enjoy anal stimulation, it might not be a great idea to "train" yourself. It's something that one has to gradually and willingly start doing. However, it does not mean that you and your boyfriend can't experiment just on him. There are plenty of people who provide anal stimulation who have never felt it for themselves, or simply didn't like it. As he is an individual, it is best for you two to explore together, slowly. It can be an immense bonding experience and you will both learn a lot together.
As for what you can do, there are numerous guides on the Internet. I don't recommend going straight for full-blown prostate massage immediately, though you likely already know that. Instead, try some external stimulation by itself at first. While it may not be widely considered as having the same pleasure potential as the prostate, external anal stimulation can be immensely satisfying. Start with that, keep it slow and sensual, and explore your feelings on the matter. It's especially good to start with something not explicitly sexual at first, like a body massage.
Simply proceed with what feels good, and communicate throughout the whole process. I'm not sure how much of this advice will be helpful, but I hope it clarifies things a little for you.