I've had some great results using Hermann Seib's excellent VSTHost

http://www.hermannseib.com/english/vsthost.htm

Along with
VSTHost Slavery Suite
On the same page.

I fire up the 64 bit VSThost with /slave
It waits for a legree to start up.

Then load the 32bit "Legree" VST into BIAB

VSTHost fires up and I can load and save different 64bit VST and VSTi, audio or midi.

You can save presets in VSTHost to recall standard setups.

You may have to manually adjust the latency. BIAB has utilities for this.

BIAB will not send over things like Tempo or where in bar or song you're in. You will not be able to do sequencers, or have delays synced to the beat. Unless your song happens to be 120BPM. This is the same behavior as for 32bit VST called from inside BIAB.

Currently I'd rather BIAB send this timing data to the VSTs than actually load 64bit plugins. Just my preference.

YMMV, BIAB 2013, Windows 7 64bit
Best of luck