Yes, you can include trapped field values as a page header when printing summaries. The caveat is that the values will only be for the first record in the data set, and they won't necessarily be related to the key values printed on that page.
To set this up, to go the summary definition. On the General tab, click the Page Setup button. Click the Change button for the Page Header, and then click the "1" button at the top right of the dialog. Pick the fields that you want, and OK the dialogs.
No, I can't envision a way in which you'd be able to easily add values from other rows for those fields into the header. Not saying that it's impossible. It just won't be easy.