Easiest way is probably to add the upload attachment control to the request offering, then put the link in the description box for the attachment. In the description editor switch to Source Edit so that you can add target="_blank" to the <a> tag to open the link in a new tab, e.g. enter something like:
Add <a href="http://www.bbc.co.uk" target="_blank">link</a> here
Thanks Joe, I actually just did this yesterday. However by putting the HTML code into the description field, clicking any link would open a blank HEAT page. By using the Category Heading control and adding <a href="URL" target="_blank">LINKTEXT</a> to the main field, The links opened correctly and it fit the length limit. I first tried the main entry in the text, number or mask field but if over a certain length the link doesn't show up visibly but is still clickable.
I think solution suggested by Joe is correct. Use CATEGORY HEADING field for the form and enter following format
<b>Click <a href="<Xyz.com>"target="_blank">here</a> to open 'AdministrationRightsForm'