I'm pretty sure that you can't.
Your progress was saved with the first computer cookies. Once you change it, every saved game will be lost.
March is soooo 8 months ago.
If you still have the old computer, you could just go there and follow this path through folders, then you look for the website's name and anything that could possibly be the game's cookiez. (I've only figured out how to do it with Windows XP, as I don't have anything else. But it shouldn't be really different.)
(You may need to make hidden files and folders viewable)
Path for XP: C:\Documents and Settings\user's-name
\Application Data\Macromedia\Flash Player\#SharedObjects\FolderWithRandomNumbersAndStuff
\Website'sName (Kongregate would be chat.kongregate, NotDoppler: i.notdoppler, Mochi: mochiads, etc...)
Screenshot (It's Papa's Taco mia there, but I doubt that Burgueria's would be really