Split PTR zone (internal and external)

[CT]

I am wondering what might be a good "workaround" for this
legacy setup...

Will do my best to explain..

IP Space
- 1 Class B Global Unique (used Externally and Internally)
- 1 Class B RFC1918

DNS Setup

External DNS     (Linux - Bind 9.8.x)
- example-ext.com     DNS domain
- authoritative for PTR Global Unique

Mid Teir DNS      (Linux - Bind 9.8.x)
- Mixture of Class B Global and RFC 1918
- not accessible "from the Internet"
- forwards all RFC 1918 PTR to the Internal DNS
- can resolve any Internal / External A records

Internal DNS        (MS DNS - w/DDNS)
- only internal DNS zones (i.e. inside.example.com)
- MS DNS use Mid Tier DNS for "external" name resolution (i.e. isc.org)
- Has the *same* Global Unique Class B PTR as the External DNS
**********************

Scenario

- internal hosts using the Internal DNS can not resolve  External PTR
for example-ext.com. since a valid PTR zone already exists..

The only solution that I have come up with is to manually
put the "external" PTR records in the AD PTR Zone file.

Not sure if there is a resolution to do in MS DNS but will ask the same
question in that group.  Wanted to start here..

Thx
CT