5
If I understand correctly, the external url is already stored in your db, has been assigned to a variable and you can display that variable as a text link on the article's page.
All thats left to do is add an iframe to the smartsection_item.html template to display the external webpage for each article.
templates/smartsection_item.html around line 27
After:
<div class="itemText">
<{$item.maintext}>
div>
Add:
<iframe SRC='<{$yourvariable}>' scrolling='no' width='100%' height='290' marginwidth='0' marginheight='0' hspace='0' vspace='0' frameborder='0'>
iframe>
Don't forget to update the module after editing the template.