help with a sliding bpm-ramp John Cage piece, pretty urgent

Hello people,

I was asked to write bar counter for Imaginary Landscapes No.4
by John Cage for 12 radios.

Basically, I am designing a counter that counts from bar 1 to bar 144, the last bar of the piece (all in classical notation) bearing in mind all the various time signature changes over the course of the piece.

The time signature changes a lot during the piece.

It starts at 128bpm, then it shifts to 88, then 144 and so forth...
It does not do that abruptly.

Example:
The notation says:
Hold 128bpm for 12 bars, then slow down from bar 13 onwards from 128bpm to 88bpm, over the course of 13 bars.
Once you reached 88bpm at bar 24, speed up again to 144bpm over the course of 9 bars.
And so forth.

I would like to use a ramp:
please go from 128bpm to 80bpm over the course of 12 bars etc.

The problem is that the line objects would not take my ticking bars as an argument, it only accepts milliseconds.

I haven't used Max for two years now and feel I need some help here.
I was asked to write it within the next three hours, the performance being tonight, that is in four hours, so I am under pressure.
Help would be really mostly appreciated!!

(Specs in case they are needed: OS: WindowsVista, Max Version: Max5)

Many many thanks,
Léah