My workaround for this is to create a group chat. I only talk to two people on Signal but I've asked both of them to message in the group chat that I've made. Now, I can answer chat messages on my nexus 5, nexus 6, and nexus 7. (I built the apk from source for the Nexus 7. I wouldn't recommend this if you actually want secrecy. I'm not doing anything confidential so I am not too worried about targeted attempts.)