well external graphics solutions do exist, but your laptop must have an express card slot available and you have to be willing to pay what these solutions cost. The
ViDock for instance ranges from $200-$300 plus the cost of a decent video card, which will range from about $60-$150 for something most people would be happy with, all the way to up $700 for the best of today. So yea, if you are looking to spend about $300 and you have an express card slot on your laptop, then yea there are some great options.
However, there are no USB graphics cards or cardbus systems that will improve your gaming performance. Another option is IF your laptop has a mxm-type expansion slot internally. Most laptops will not have one unless they already come with a dedicated graphics card...which yours does not have...HD 3100 is an integrated solution built into the motherboard chipset.
So really, if you cannot afford the external option then you are pretty much out of luck. According to the
official site the MINIMUM requirements call for an Nvidia 9600 or ATI HD 2900 series. Though these are old cards, today's equivalent will fall in the $60-80 range. The recommended graphics cards are not listed but are likely into the $150-$200 range depending on how high a resolution you wish to play and what you consider acceptable frame rates and detail settings.
Your HD 3100 do not come even close to the minimum graphics requirements so really your only options are going to be to invest a couple hundred bucks in external graphics (IF you have the express card slot), buy a new laptop (which you already ruled out), or just wait 8 months for the PS3 version.