Is it possible to make a larger bike fit a smaller person?
A couple of things to tide you over:


Obviously, put the seat down as far as you can. If the post can't go any lower, you might see if you can get a shorter post, or have the current post "chopped" to a shorter length (although that will probably cost you).
Move the seat as far forward as possible. To do this, you loosen the seat from the post using a hex-wrench; move the seat up, and then tighten back up. To really get the most possible, you can even try tilting the seat forward, although this might leave you feeling like you're sliding off of the bike (this is what my wife did to fit into her antique 3-speed).
You can loosen the handlebars and turn them upward, so you're not as stretched over the frame. To take it one step further, you can remove the handlebars, turn them around, and put them back on backwards ("bull horn" handlebars), but that will require re-taping and doing some more serious cable adjustments. It sounds like you just want to make a quick fix without too much work.


In general, being 3" too short for a bike probably isn't too bad. All of these fixes will lead to the overall fit changing. Stay on the lookout for someone who looks a tad too small for their own bike, and maybe you can engineer a trade at some point!