That's not what hotlinked means. Please don't refer to it as that.
I don't have OpenOffice installed right now, but isn't it as easy as highlighting the text you want to make into a link, clicking the "hyperlink" button (which looks like

or something like that), and then filling in the URL you want to link to in the Target field? I would guess that gets preserved through export to PDF. Maybe someone can confirm.
EDIT: Update: Actually, I'm not sure the hyperlink button looks like that anymore on newer versions of open office; It may look like a globe on a page or something like that instead. If it's not obvious, you should be able to find "Hyperlink" in the "Insert" menu, if I'm not mistaken.