That's a better question for XDA Developers. If anyone figured it out, it's them. I'm guessing you'll need to do some serious hacking, and then the experience will probably be crap because of the low-res screen and slow processor/lack of RAM.
Or you can make a CALL with your L900 into Microsoft store also.Another thing u may try is use www.google.com.Your question typed into Google shows me something interesting: http://mashable.com/2012/06/25/lumia-why-no-upgrade/
And good luck with exploring the newcomer of the next year - THE INTERNET