from personal experience it can be rather painful, as the tissues under the nipple get VERY tender and sore. But to each their own :)
Easiest way to see if you are prone to it would be to cut your hormone levels down to damn near nothing for a few weeks to a few months, then back up to normal. This would somewhat simulate the hormone surge that accompanies late pregnancy and could spark lactation. I had something similar happen when I was unable to renew my prescriptions for a quite a while then went back up to a full dose.
There are other drugs that can simulate this, and may spark lactation. However I do not know NEARLY enough about them to feel comfortable providing any advice on them.