tweaking Articulation grobs - fermata / Slur collision

[Farmer, Pete {PGLC~Basel}]

A recent lurker, first-time poster writes:

Dear Han-Wen and Jan,

First, thank you for writing such a wonderful program, and so generously making 
it available. The lilypond output is truly beautiful, and I haven't found any 
commercial software which can rival lilypond or your lovely feta font.

I've been able to get quite far with the existing documentation, but I now find 
myself stuck, and have not seen this specific question covered on the mailing 
list. (Please forgive me if it has, I've only been reading the list for two 
months)

Here goes...

As you will see, my fermata collides with a slur and a tie. I would like to 
raise the fermata slightly, as is easily possible with other grobs (ex. 
BarNumber and the padding parameter).

As best as I can determine, the fermata is not really a grob, but part of the 
collection of Articulation grobs.

I've found examples of using ^ and _ to force positioning of these elements, 
but so far have had no joy in using them with the fermata.

I would like to avoid forcing the slurs to below, and have seen the raised 
fermata solve the problem in professionally typeset music.

Grateful for any clues, and thanks again for making Lily,
Pete Farmer

%-------------------------------------<snip>------------------------------------------
global = \notes {
        \time 4/4
        \key g \major
        \clef "bass"
}

part = \context Staff \notes \relative c {
        c, a'(d)fis a(cis)d8-\fermata()d16 a, b c d e fis g
}

\score {
        \context Staff = solo {
                \global
                \part
        }
        \midi { \tempo 4 = 80 }
        \paper {
                linewidth = 18.0 \cm
                interscoreline = 3.0 \pt
                interscorelinefill = 20.0 \pt
        }
}
%-------------------------------------<snip>------------------------------------------