I'm fairly certain that RealSinger's synthesis engine is something like the same technology used for Vocaloid1, although probably on a smaller scale (and implemented into a software that's painfully difficult to use). There are some times when people successfully tricked others into thinking they imported their voices to the Vocaloid1 engine by providing samples with RealSinger.
It can be pretty tricky to get it to sound good. When I was doing experiments with it last year, I managed to get my sister to record an American English bank, and did a cover of a song she chose.
I was able to render all the vocals for the song because it's incredibly repetitive. So I only had one of each lyric section in a MIDI, then I recorded the output with Audacity+Stereo Mix. For a longer or more complex song, it might take multiple MIDI to get every lyric, since you have to close+reopen the program after the trial has been used up.