Parenthesize slashed grace with fingering?

[Colin Campbell]

In transcribing some cello exercises, I need to show a slashed grace note, with a fingering, in parentheses.  The exercise involves shifting between first and third position on the same string, so it emphasizes the intermediate "target" position, with the intent that the grace note gets eliminated as the shift gets smoother.  The following gives me all I need except for the parentheses.  I'm a bit foggy from a virus, and I cannot find the magic incantation which will show both the grace note and the parenthesis. Using 2.17.10, by the way.
%<%<%<%<%<%<%<%<%<

e'2-1 ( \parenthesize \slashedGrace gs8-1 a2-2

%<%<%<%<%<%<%<%<%<

Any pointers to TFM or LSR gratefully received!

Cheers,
Colin

-- 
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You need to be able to throw something back. 
-Maya Angelou, poet (1928- )