I want to be able to get the value/element (TableCell?) at the location of the context menu invocation. That is, right click on a table cell element and be able to perform operations based on that. (TableCell is not valid for CustomTool<TableCell>, so alternatively making that available would also work.)
Have you tried this:
Available in the context menu shown when right-clicking a cell in the table.
https://community.tibco.com/wiki/create-custom-tool-tibco-spotfire#toc-15