They add a special endorsement.

This insurance carrier would then add an endorsement on the second unit to cover the exposures of the Short-Term Rental (STR). 

I don't like to post endorsements on here but if you're still interested I'm happy to share who I usually buy from.

A mortgagee clause and/or loss payee endorsement relate to the property and a PM doesn't have a insurable interest so they would not be included in any sort of property claim settlement.

Another ringing endorsement of California's (un) justice system.  

So the POA serves sort of as a substitute for endorsement.  

All, please be aware that Aj does get paid to endorse martel, but he does not disclose this information. 

But, it has an exposed blade so if you're not skilled or comfortable with that use, probably better to go with something easier to control.BTW - I'm not endorsed by nor do I specifically endorse Dewalt tools, though I wish I was 

If they endorse this strategy for you, then start searching for a provider like @Yonah Weiss or @Julio Gonzalez or maybe pursue a DIY option mentioned by @Basit Siddiqi.

Note this is not an endorsement of their investment offerings.