No need for a macro, click on Edit - Comment Add after selecting the block. If it is greyed out, your syntax highlighting language for your current file does not have a Line Comment = entry.
But I would rather prefer to avoid to copy the selected text in the clipboard. Is there any other way to do that?
I would also uncomment the text if no text is selected and the mouse cursor is between /* and */ with the same macro. How can I do that?
Here is a macro which works only on a selection without a template and automatically detects if the selected block is already a commented block (contains /* anywhere) or not.
It is not possible to restrict the search for /* to only start of the selected text. But you can use a regular expression search for "/*" with additional regular expression characters if you want to restrict it a little bit.
Disadvantage of this solution: It works only for blocks up to 30,000 bytes.