defintion for metrelessness (help?)

[Monk Panteleimon]

I have a little definition (here called "chant") which, together with my 
standard \layout
block let's me write unmetred music ad infinitum without having to 
(explicitly) add
invisible barlines whenever I want the line to break. This
potentially really useful, since otherwise I have to recompile my .ly's
often, decide where the break is best and put it there.

There are a couple of problems which keep me adding the explicit \breaks
amyway, however, and if anyone could help work them out I would be so
happy that I would submit my definition to the LSR without delay.

(ahem..) The definition:
%%%%%
chant = {
       \set Score.defaultBarType = ""
       \override Score.SpacingSpanner #'strict-note-spacing = ##t
       \set Score.barAlways = ##t
       }
% and in the layout block (but this part's not at issue) :
\layout { ragged-last = ##t
     \context { \Staff
         \remove "Time_signature_engraver"
             \remove "Bar_number_engraver"  }
             }
%%%%%

The problems with the "chant" definition are 2, so here's the probably
harder one first:
I want the linebreaks to be just slightly more picky, something like
what happens with Forbid_linebreak_engraver (sic?) only referring to
what the adjacent note values around the break, so that:
1. Lines don't break between notes of duration shorter than a quarter-note,
e.g. between a dotted-quarter and an eighth and
2. Lines don't break in the middle of a melisma whose whole duration is
less than one whole-note.
Possible?

N.B. I am aware that I could just set the t.signature for some
denominator higher than 8 (rather than doing BarAlways)
The problem with this is that Znamenny Chant is so metrically
irregular and syncopated that I would be getting bar-overflow all the
time. It wouldn't fit even into a 1/4 t.signature.

I'll leave the second problem for another message.
Many many thanks.
--
Monk Panteleimon
Hermitage of the Holy Cross
Wayne, WV, USA
http://www.holycross-hermitage.com
http://www.holycrosskliros.org