RTC shell client: using external compare tool and built-in tool for different type(extension) of files

RTC4.0.4/4.0.5 and Windows Shell client used.
There is a need to use self developed custom compare tool for a specific type of file only and all other type of files, they intend to use RTC embedded compare tool(custom tool only support one specific type of tool). Windows shell client is considered at this moment.

However, in Windows shell client > manage preferences > compare tools, it only has option to add the external compare tool. Once the external compare tool is set, the user can only use it or built-in tool to compare the versioned files. There is no option to open the specific compare tool(external or internal) for the specific file.

Is this achievable in Windows shell client?

I notice that in Eclipse client, there is two options in the context menu in PendingChange view:
Open in compare Editor (I think this is the embedded compare tool)
Open in external compare editor

Although I don't find an automatic way to make the two editors for the specified file types, at least it seems that the user can use the option to open the file in different compare tools in Eclipse client.
I am wondering why the same menus are not available in Windows Shell client. Is that I did not find the menus
in shell client or it is actually not existing as Eclipse client can do or there is any way to achieve the same in the shell client? Thanks