Hi Paul,
How about :
%%%%%%
\version "2.14.2"
DB = \downbow
UB = \upbow
DUB = -\tweak #'outside-staff-priority #0
-\markup {
\musicglyph #"scripts.downbow"
\hspace#3 %% <= set space
\musicglyph #"scripts.upbow"
}
UDB = -\tweak #'outside-staff-priority #0
-\markup {
\hspace#4 %% <= set space
\musicglyph #"scripts.upbow"
}
\relative c' {
\time 6/8
\clef alto
% measure 27
\pitchedTrill
e'2.-2~^\DUB\startTrillSpan fis
% measure 28
e2.~^\UDB
% measure 29
e2.~\DB\stopTrillSpan
% measure 30
\pitchedTrill
e2.~\DB\startTrillSpan f!
% measure 31
e2.\stopTrillSpan
% measure 32
\bar "||"
}
%%%%%%%%%