Rigidbody sleep used to be implemented in tyFlow but PhysX implementation of it has weird quirks (that the PhysX devs have acknowledged) which can cause more problems than they're worth.
For now you can manually switch between kinematic/dynamic using filters on operators whose timing is set to continuous. Below a certain velocity magnitude put the objects to kinematic (you may also want to dampen/stop their motion using Slow/Stop operators with the same filters applied) and above a certain magnitude convert back to dynamic. Won't work exactly like sleeping (they'll wake up from tyFlow forces but not PhysX inter-particle collision forces), but may be enough to suit your situation.
For now you can manually switch between kinematic/dynamic using filters on operators whose timing is set to continuous. Below a certain velocity magnitude put the objects to kinematic (you may also want to dampen/stop their motion using Slow/Stop operators with the same filters applied) and above a certain magnitude convert back to dynamic. Won't work exactly like sleeping (they'll wake up from tyFlow forces but not PhysX inter-particle collision forces), but may be enough to suit your situation.