The Printable View skin is very basic so you shouldn't need to force compatibility view on it. Instead, figure out why it's not working correctly in IE and fix the issue. Compatibility View should always be used as a very last resort.
The problem is probably with and overflow: hidden rule in the CSS somewhere. Without seeing your site, it's hard to tell though. Best thing to do is open the site in IE, view the printable view and then open the IE Dev Tools by pressing F12 on your keyboard. Use the Element Select tool to select the page and then start looking through the CSS style listed on the right for anything that may be causing the scrollbars to not show up. If you don't see anything, start selecting different elements in the markup on the left and then check the styles associated with those elements. Once you find the culprit, make note of it and then remove it from the printerfriendly skin inside of \data\sites\[n]\skins\printerfriendly.
If you have trouble with that, and you're using a relatively new version of mojoPortal 2.4.x.x or higher, copy the printerfriendly skin from \data\skins to data\sites\[n]\skins. Now you'll be using the latest version of the skin so maybe that'll fix the problem.
Also, if you're using IE 8 or older, you really just need to upgrade. Even if you're using IE 9, you should upgrade. I know the corporate world doesn't like to upgrade IE but they never treat the other browsers that way and they should just get over it. :-) /end rant.