I'm using the current Mac version which has recenelty been upgraded to Beta 2.

In Beta 1 I managed to set up a snap option of "between two points" and found it very useful (otherwise you have to draw a temporary line and select its midpoint).  

I can no longer find the command.  Can anybody help me locate it?

One of the irritations with these beta upgrades is that all your settings get lost.  Hopefully, when DS comes out of Beta all that will improve.