He'd have to get the permission of the prison authorities.  Unless your aunt had named him as her health care representative, in writing, that's probably a long shot, and maybe so even if she did that.  The problem is that he's a boyfriend, not a husband, which makes a large legal difference, and that prison authorities' job descriptions don't include being great humanitarians.

If you can arrange for your aunt's doctor to accept a collect call, at whatever time the boyfriend has telephone privileges, it might be possible to take care of this within the prison routine.  I wouldn't hope for a temporary release or a visit under guard, although it doesn't usually hurt to ask.