Your best option is to work with your current lender. It's unlikely that they want you to default on your mortgage, or will call your balloon payment due without being willing to discuss other options if you have no equity. It makes more sense for them to offer you a modification of terms on your mortgage, or an extension of the balloon payment period at the very least. You may need to show them that you had to relocate for a job opportunity, or some other valid reason. They may offer you a short refinance, a loan modification (yes, you can get modified on a former principal residence if you had to relocate), or they may offer to do a deed in lieu, or work with you on a short sale. Any of these options may be preferable to defaulting on your former principal residence.
Contact a HUD approved counselor on the makinghomeaffordable.gov website, and discuss your options with them.
And finally, be certain that your current mortgage situation on your new home is secure and fixed before taking any action that might cause any negatives on your credit rating, or flag you as ineligible for a refinance on your new home if that would be best, first.