Do you have the right of abode in HK? If so, then you can probably try to get into PolyU, which accepts many students on a part-time basis on a pretty lenient basis. It's part of their continuing education scheme for working people, which is why it's part-time.
But, if you don't have the right of abode in HK, I highly doubt you can study in HK part-time.
That's my understand of the University system here. But I could be wrong. You should check it out.