In my Application Object, I created properties for each manager
class:

oApp.cWindowsMgr = "MyWinMgr.Vcx"
oApp.cSecurityMgr = "MySecurityMgr.Vcx"
oApp.cMenuMgr = "MyMenuMgr.Vcx"

Then if I want to subclass any of the manager classes, I can specify the new class library. In my oApp.SetupClasses() method I have:

IF NOT EMPTY(This.cWindowsMgr)
PUBLIC oWindows
SET CLASSLIB TO (This.cWindowsMgr)
oWindows = CREATEOBJECT("WinMgr")
ENDIF

The only catch is that the subclassed windows manager must have the
same name as the original windows class. Other that that, it works
really well for me and is extremely flexible.