I think it can be acheived using access controlled policies (ACLs).
Provide deny access to SoftType in context/container where its not applicable
Provide deny access at level where this Object is defined (Site/Org) and provide Create/modify/etc access in desired context/container.
If ACL's are applied correctly (Create/Modify/etc deny access by Role) then Soft Type or Object will not apear on User's create window.
In Reply to Mike Lockwood:
ACLs work but the user doesn’t see the result until they select Finish on the New Doc wizard.
Using OIR’s with Lifecycle has the advantage of removing the type from the list of types to select.
Please refer below example (tried on 10.1 M040)
After adding this ACL user (wcadmin) was not able to see Document Type into Create Doc window
I hope this example will help.