File association with application where file-extension is not defined in plist file

Hi, We are developing a Business Management application for Accounting/Inventory/Invoicing etc. which is capable of being integrated with a reasonably wide variety of 3rd Party document formats – like spreadsheets, and PDF, and ALSO capable of being customized by the end-user to support additional formats.  While the ‘out-of-the-box’ integrations(extensions) can be listed in the info.plist for people to opt to open a particular document type using our application, if they wish to – what do we need to do to allow them to associate their own customized integrations.  For defining the same in plist file, we do this for already defined extensions :

<dict>
			<key>CFBundleTypeName</key>
			<string>TWDB</string>
			<key>CFBundleTypeRole</key>
			<string>Viewer</string>
			<key>LSHandlerRank</key>
			<string>Owner</string>
			<key>LSItemContentTypes</key>
			<array>
				<string>com.tw.twdb</string>
			</array>
</dict>