I see I needed to nose around their site more. I dug into the forum and found someone else asking about "central" mode. The answer is that the Blend Micro can't run in "central" mode but that the Blend Nano can. :) But the software for this is still in Beta testing. :(
The nano does solve one problem for me. It has 11 I/Os which might be enough for my app without adding a port expander.