"Maybe nothing short of a big BEGIN FLASHBACK would do the trick. DX"

better idea: How about... uhm... a short line to establish a change of time AND place: something like:

Venice, 1706...

Sacred Mountain training ground, 3 months ago...

A village lost in memory, 10 years earlier...

Or even just: 10 years ago....

I don't think i'ts quite as smooth as .. well.. what it sounds like you're trying to do... but maybe people would 'get' that hint...

or failing that... do something funky at the start of the chapter like:

///// = start flashback
\\\\\ = end flashback

So that all you have to do is /// or \\\ and people will 'get it'... or something ^^;