There is no need to include the non-resident spouse on a resident alien taxpayer's application for automatic extension of time to file a federal tax return. 

The non-resident spouse is not yet required to file a tax return, and the  resident alien taxpayer does not have to declare a filing status (MFS, MFJ) with the request for extension. Since it will ultimately be a joint return, you can request the extension yourself.

If you don't feel comfortable with this approach, you can    print out Form 4868  from the IRS, fill it out, and mail it on or before April 18. Complete mailing instructions are on the printout.