As you probably know by now the Microsoft Surface does allow some flash content, however at the current moment there is a whitelist of websites that are allowed to use the flash plugin. There is a way around this problem however as long as you don't mind getting your hands a little dirty, this tip comes from some clever guys over at XDA-Developers. First of all you'll need to attach your keyboard to the surface, if you don't have a TouchType keyboard then you can just use a regular keyboard.
Open the desktop version of IE 10, you can do this by tapping on the desktop tile and then tapping on the IE icon in the bottom left hand corner.
Hit Alt on the keyboard, then on the popped up menu hit “Tools” and then “Compatibility View Settings”. You will then need to UNCHECK the last check-mark which is named “Download updated compatibility lists from Microsoft”. If you fail to do this then next time you restart your Surface you'll find that your settings have been overwritten to the default again.
Hit Windows Key & R, this will bring up the run menu and then Copy and paste the following into the text box and finally hit the OK button.
notepad "%HOMEPATH%AppDataLocalMicrosoftInternet ExplorerIECompatDataiecompatdata.xml"
You'll now need to find the <Flash> tags in the text file, and within those you'll need to enter the domains in which you want to allow flash to work. Using the below template add in any domains that you wish to enable flash on for example you may wish to enable flash for Google, to do that enter google.com as the domain inside of the tags such as below.
After you have done that you'll now need to return to the Metro IE (hit the windows key to return to MetroUI), and then hit Windows Key + I to open the settings menu. And finally tap “Internet options” and “Delete browsing history”
Now you should be able to use flash on the sites that you entered in the text file, you can continue to add more and more domains to this file but remember that you must delete the browsing history each time you update that file. If you need further information on this topic then visit this forum thread for more advice.