Here is one solution I came up for a customer:
1) Add another web site to the Exchange CAS (OWA) server such as owamoss.colotech.edu
2) Added in a second /owa vdir to the new website you just created (e.g. owamoss.colotech.edu) via Exchange command shell:
New-OwaVirtualDirectory -WebSiteName "owa.moss.colotech.edu" -Name myowa2
3) Change the new /owa vdir in the new website to Windows Integrated
4) In SharePoint, point the SharePoint OWA webpart to the new website name (e.g. owamoss.colotech.edu).
Only use this new URL for MOSS webpart rendering and other users will continue to use the current URL for OWA such as mail.colotech.edu