Add a temporary number to iMessage

I am traveling outside the US and have got a temporary local SIM. I realized that once I activated the local SIM, that my iMessage was no longer associated with my actual phone number and so I was not able to get any texts from my friends.

I understand why the activation works how it works, but is there a way to temporarily add a number to iMessage. Or put it another way, is there a way to keep my default number associated with iMessage as-is and not lose it when I add a local SIM?