I currently have JL F ORD-HND and another JFK-HND that I want to make originate in SEA/PDX instead. In other people's past experiences, is it possible to add on West Coast to East coast gateway-HND?

Doing a multi-city or one way search it doesnt come up. But in the past I've been able to ticket HND-ORD-SEA-RDU, so my desired ticket doesnt seem like extreme backtracking in comparison.