This is something that was discussed as a possibility recently, when Mike Vick reworked his own similarly-structured deal. Jason from NYJetsCap.com discussed some of the potential ways to bring down his 2013 cap hit here.
Since Holmes has guaranteed salary, it's possible the Jets could make a minor tweak to his contract to save a small amount of cap room without actually affecting the amount owing to him or committing themselves to guaranteeing him any additional money. Alternatively, they may be considering freeing up a more substantial amount in 2013, which would likely require them to increase his 2014 guarantees and cap number.
If the Jets don't restructure his contract in 2013, they could potentially release him in 2014 and generate a cap saving of over $8m. They may effectively be looking to cash in some of that potential saving now, without completely committing themselves to him beyond this season.
Following the recent releases, the Jets are currently estimated at approximately $7m under the projected cap, although reports did emerge this week that the cap could be $123m - over $1m more than previously expected.