Attach two PBDCloth

[monkeygame]

How can I connect two pbdcloths in the same particle system by creating a new constraint/attachment, so that they are linked together and have realistic mutual movement effects?
I tried adding a spring between them, but found that one constraint cannot connect the particles of two different cloth objects. Because this constraint only takes effect when added to a certain cloth. Are there any other solutions?
Exclusion: The solution of connecting the two cloths through a very small mass rigid body is not what I want.