If you are arriving in the US from Europe next spring, you should be eligible for Enrollment on Arrival. This allows you to complete your enrollment interview at the CBP location where you enter the US. Most major US international gateway cities have this. The link has all the locations and the hours. You will not be able to use GE when you arrive but you will have use of GE and TSA Precheck once you complete your interview and are approved.

Here is the thread on the Trusted Travelers forum that specifically discusses this and any related issues.

Global Entry Enrollment on Arrival