Ranging from the worse forms of guides/documentation to the poorest of support and so I heard, I actually begin to suspect Rigol is more like marketing house than any true instrument developer / manufacturer. And for that reason, I am not going to buy any Rigol, no matter how cheaply they will have on offer.
The firmware is just like the secret keys and if there are no leaks, no schematics, I am afraid no one here is able to crack it.
I understand your distress. I am sorry, I am not able to help.
You should write to the Manager or CEO of Rigol. But I doubt, like a marketing house or profit entity, they would bothers to help, otherwise they would.
Good Luck.
Edit: I contacted Rigol China, and they are great people there and they quickly provided the solution to the problem of the DG1022.