Yes, it is possible.
With the two page 8.5x11 PDF open visit Print Setup.
Select a paper size of 11 x 17 and an orientation of landscape.
"OK" out of the dialog.
Select File > Print.
In the Print dialog use the drop-down menu for Page Scaling to select "Multiple pages per sheet".
From the Pages per sheet drop-down menu select "Custom... 2 by 1".
From the Page Order drop-down menu select "Horizontal".
--| Screen capture is of Acrobat 8's Print dialog. It'll be similar for Acrobat 9 or X.

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Be well...