metric modulation problem

[libero . mureddu3]

(Sorry if this message was already sent, I had problems with the mail)

Hi,
I am trying to put a metric modulation mark, but I cannot find a way to achieve
it:
so far I have:

{a1 \mark \markup { \tiny \note #"8" #1 "=" \tiny \note #"8" #1 } a1}

but I would like to have the bracket and the number of a tuplet above the
first eight symbol, to show that the previous eight notes within tuplets,
are, in the new tempo, equal to simple eight notes.
You can have a look on those web pages:
http://hometown.aol.com/loudfonts/TempiFnt.htm
and
http://www.dimusicengraving.com/metric_modulation.htm
any suggestion?

Regards,

Libero Mureddu

lilypond 2.7.10
macos 10.4.2