There's an easy way, but it depends upon the transceiver you're using. Some transceivers have a receive antenna loop - on the rear panel there would be a jack for receive out and one for receive in. The two would normally be jumpered together. With that type of setup, you could build or obtain an HF splitter (Clifton Laboratories has a low price kit) and feed the receive out line to the splitter input. The splitter output #1 would go to the transceiver receive input and the splitter output #2 would go to the SDR antenna input. This would drop the receive signal by 3 dB in each receiver, but that's really of no consequence. That's what transceivers with two receivers do anyway. With this arrangement, you don't have to worry about protecting the SDR on transmit.
73, Floyd - K8AC
Yep. Per Elecraft:
Yes, that will work without any changes to the rig. Just connect the other rig to the RX OUT bnc and turn on RX ANT from the front panel.
73, Gary AB7MY