If you have your own directly registered IP block, we wouldn't be having this conversation as you would already have a resolution routing solution upstream else you would not be able to map any of your IPs locally to your server in the first place.
Let's take a step back here for a moment ....
What is your issue that you are actually running into?
I got that you are trying to hide reference to your upstream from your clients, I get that really --- just don't see the reasoning behind it as I could always tell you who you purchase from and who they purchase from and all resellers in between irregardless of how you set things up and nothing you could really do about that and the areas you are trying to mask would not be something every day average users would even look at let alone understand; thus, you are trying to mask the IPs in an area where it won't really have any impact because the only people who would think to look there would know how to find out the real details about everything totally irregardless of what IP you setup in there.
What I would concentrate on more heavily is your actual DNS servers you use with your domains and your clients and make sure those are using your CIDR block and setup PTR records on each IP in your block that maps back to hostnames on your own domains. Those are the areas that will make the most difference with your average users.
Now do you understand what I am talking about?
Now taking this to a different viewpoint being technical, there is no technical reason you could not use your own resolver provided that DNS server was
NOT located on your hosting server, allowed zone transfers between your servers and that server, and that resolver in turn DID in fact subsequently map to other external resolvers at your upstream provider and outside your network then you would be able to use your own resolver as an intermediary in that case.
Hope that helps
PS: I do know everything! LOL
