I haven't been able to, but from what I understand yes we can by stimulating and massaging the prostate gland. I just don't have the patience, although its plenty pleasureable to do that while masturbating, leads to quite the orgasm/ejaculation.
I haven't been able to either, and believe me I've tried!
However, I have been able to 'milk my prostate' which forces prostate fluid out of the penis, which basically looks like the white part of ***. Its not ejaculation though, and certainly no orgasm. Felt interesting, but not great, so I don't bother with that anymore.
I've heard that some guys can orgasm from just anal and prostate stimulation, so I guess some are more sensitive in that area than others.
Anal stimulation 
