You are awful far off for them to do much of a deal. You probably have most of a year to go on your current contract because the upgrade date is a couple of months before your contract end-date. They do that so they can start tempting you with a new phone (and new 2-year agreement) before you are free to switch to another carrier.
You could try asking VERY nicely... tell them you're very interested in the BlackBerry and are ready to move to a nice juicy data-plan... but you just can't justify paying the big up-front cost... is there maybe SOMETHING they or their supervisor could do to get you the better price now since you realise that it will add another 2-years to your current contract and make sure you stay a loyal (and profitable) customer? You get the idea.
If that doesn't work.. wait six months and try again. Once you get closer to January you can say "well, I guess if we can't work anything out I'll just sit-tight and see what Sprint has to offer once my contract is up." They waived a bunch of fees and allowed me to change the end-date of my current contract once I was three months short and made it clear that it was "deal or lose me" time.
