I'm a little confused as to why this question from 2015 is on the front page of Hacker News. The answer (which may not have been available at the time) is "get a family account, which allows multiple simultaneous streams".
It does not (directly) allow multiple simultaneous streams. It allows multiple simultaneous users. This means setting up a dummy google account for each device that you wish to have play simultaneously, which is a bit of a pain.
Ideally it would be more Netflix-style, which puts a limit on the number of devices but does not really care about "identity", though obviously sharing the password to your Google account is a non-starter for family sharing cases.
Ah, I didn't scroll that far down in the comments. AFAIK, yes, the family plan still only allows one stream per user. But in the situation outlined in the question you'd just use a different account on the Google Home than you do at work.
Ideally it would be more Netflix-style, which puts a limit on the number of devices but does not really care about "identity", though obviously sharing the password to your Google account is a non-starter for family sharing cases.