Conversion to Roth IRA - Extending Federal Return

[Yardley CPA]

MFJ couple converted traditional IRA's to Roths during 2010 and deferring tax to 2011 and 2012. Extending Federal return to determine if value of converted Roth's decrease in value prior to 10/15. New Jersey State return has $2,000+ refund. Can I efile the New Jersey State Return alone? Taxpayer prefers to have refund than apply toward next year.