This is commonly called "2-up" page placement, and, no, k2pdfopt cannot do 2-up page placement by itself. Sorry. But you can run k2pdfopt in "fit-width" mode with the width and height of the output page set for normal portrait like so:
k2pdfopt -ds 2 -w 8.5in -h 11in -mode fw -ls- ...
This will strip the margins and create 8.5x11-inch pages. (The -ds 2 scales up the source document so it will fit the full width of a portrait page.) Then you can use CutePDF's print-to-PDF driver (free download) to print that 8.5x11-inch PDF 2-up by selecting 2 pages per sheet in the printer preferences.
Or you can use Coherent PDF's command-line tool (free for personal use). In this case, I use cpdf's -twoup-stack option, so I want the k2pdfopt output pages to be exactly half the size of an 11x8.5 page.
k2pdfopt -w 5.5in -h 8.5in -mode fw -ls- myfile.pdf
cpdf -twoup-stack myfile_k2opt.pdf -o temp.pdf
cpdf -rotate 90 temp.pdf -o final.pdf