In FitNesse, can variables be defined in terms of other variables?

I want to do the equivalent of:

    int a=3;
    int b=a;

To make this concrete, I have a variable defining the date:

    !define clock.date {2/2/2009}

I then want to define some other variable ${other.date} based on it, something like:

    !define other.date {=${clock.date}=}

However, this doesn't work. Is there any way to do this?