Okay first off a PCI Express is a 'slot' inside on the motherboard on DESKTOP computers, this is a Laptop not a true Tablet (http://www.cnet.com/laptops/lenovo-thinkpad-x230/4505-3121_7-35313302-2.html) and is made for business purposes AS SOLD. It is NOT MADE for gaming purposes, if you needed a 'portable' gaming platform then you needed a laptop with a dedicated SEPERATE GPU built into it for gaming (and adding on a significant cost as well to deal with heat, lighter weight, etc.)
That said, I think your 'thinking' of using the ExpressCard (http://en.wikipedia.org/wiki/ExpressCard) External Video Card as your solution that was suggest three years ago to solve similiar situations as yours before manufacturers INCLUDED the video card inside the laptops. That also is the problem, there is no support for this solution anymore and is considered a DIY Hack (http://www.harmonicinversion.com/index.php?product_id=191&page=shop.product_details&category_id=1&flypage=shop.flypage&option=com_virtuemart&Itemid=6&vmcchk=1&Itemid=6 http://hackaday.com/2011/10/19/beefing-up-your-laptops-gaming-chops-with-an-external-gpu/ ).
The worst problem is, the current set of video cards out there all need higher power then comes 'out of the box' with desktops, and with the 'low power consumption model' for laptops it is impossible for them to power these cards 'out of the box'. So this gets to be even a harder solution to wire up a external power to the external card wired externally to external LCDs and ISN'T setup to be 'portable'. This leads to ALOT of risk that a electrical short can happen (which will FRY your Lenovo), something being bumped and broken, and so on.
As you suggested, your REAL solution is buying the proper device (a portable gaming laptop) to meet your demands, or adjust your demands (laptop for school /work, game console to 'game on').