How to add "include closed" radio button

Part of building a portlet includes giving the end user the choice of displaying closed requests as well as open requests. This behaviour is not provided by default and therefore needs to be added by the developer.

Approach:
1) Add a new field called "Include Closed?" in the request type. There is no need to display this field so make it invisible across all statuses.
2) In the data source, there is no need to add the field in.
3) It is necessary to add a filter that will handle this. See the image below for details:

This filter is providing two options. Either display:

1) requests with a token (INCLUDE_CLOSED) value set to "Y"

2) OR all statuses apart from %CLOSED% and %CANCELLED%