You probably know how to use the mailto command for quickly linking to one email address. You can not only link an email address but subject line as well.
Just highlight the text you want to put mailto link on, click on the hyperlink icon and type in the right text.
The link text should be:
Use the usual mailto: and then enter email address. After that add ?subject= and then follows the subject line that you chose. Between every word use %20 as a spacing between the words.
You can find more about mailto options to use here.