You can apply for an ITIN for your spouse for 1 of two reasons: because you are married and wish to be able to file joint tax returns in the future, or 2) have the need to file a tax return in the present and need a tax ID number for that tax return.
In your present situation there is no requirement for a tax return to report your spouse's foreign income.
You can file a tax return with an W7 ITIN application.
Filing the ITIN application with the tax return is the most common way to request an ITIN.
You would not file Married Filing Separately and include any of your spouse's income on that return.
Application for IRS Individual Taxpayer Identification Number Supporting Documentation for ITIN Application (see p3 col 2)
