How to select which number to message when contact has an iPhone and an android?

My husband has an iPhone for work and an android personal phone. I have both of his phone numbers under one contact. Before I updated my phone, I had two separate messages for his two phone numbers. Now they are merged. This is fine, but I want to be able to select which number I am messaging. It seems to always default to iMessaging his iPhone, even when the last message in the conversation is a text from his android. Even when I try selecting his android number in his contact card, it will still switch back to iMessage. Does anyone know a work-around for this, other than putting in separate contact cards for his two phone numbers? I like having them merged, I just want to be able to select the right number?!