collation tailoring using before

[Martin Hosken via CLDR-Users]

Dear All,

I am trying to tailor (for the sake of argument) \u0300 to be primary ignorable and have a secondary collation key less than that of a primary character (a).

I tried:

&[before 2][first primary ignorable] << \u0300

But then I get CEs of this form:

a	[2900.0500.0500]
\u0300	[0000.8000.0500]

I'm wondering how I can get \u0300 [0000.0400.0500].

TIA,
Yours,
Martin