The last time I checked you could do this with the reseller account permissions. I do not see that being that hard. If you set up your package in whm to have two ip's and their own nameservers. Then enter it into modernbill as just a package you should be good to go.
Unless I'm mistaken, all MB does (and other panels as well) is send over the IPs to the client. It's still up to the host to create the A entries manually.
As for giving 2 dedicated IPs, then it's impossible.
Modernbill does all the A records and account creation on the server. You may have to make a script yourself to add the ips to the reseller account as mb may not be able to do this.
It can auto provision IPs but its not really done on modernbills side. When you create a cpanel package, it'll contact the cpanel server, asking for a dedicated IP to be assigned to the new account. If that new server has IPs to provision, then it does so automatically.