Help with extending my L visa

I am currently on a 30 day L type and my partner is getting a Z type & I am going to be attached to her Z type with an S1 type. Is there a way that I can extend my L type for a short time with out having to go back to HK I have checked with the Entry /Exit buro and they have said that I need to have a lot of funds on me to extend the visa with them. I dont currently have those funds.

Is there an agent that can do the extension for me or is it better to go back to HK to do it.