This is one of the reasons I got a longarm! Actually, many long arm quilters do offer a sandwiching service. They use a really long basting stitch. My machine came with one built in specifically for this purpose.
Other than that Sharon Shamber's board basting:
https://www.youtube.com/watch?v=bhwNylePFAA
and patsy Thompson's wall basting:
https://www.youtube.com/watch?v=2UoUzK19Vww