A service provider runs a next-generation multicast VPN using mLDP as the multicast transport. For a VRF carrying several high-bandwidth video sources, the design team wants each PE to build a P2MP LSP toward only the PEs that have interested receivers, avoiding delivery of high-rate streams to PEs with no receivers, while still using in-band or overlay signaling to trigger tree creation on demand. Which mLDP-based MDT construct meets this requirement?