[tabular] Only align *first* equal sign

Hi,

to align my code I use the tabular plugin. How can I align only at
the first equals sign? Example:

alpha = gamma // number=first
foo=bar // another comment
one=one

If I run Tabularize /= it comes out as follows

alpha = gamma // number = first
foo = bar // another comment
one = one

How can I avoid that the equals in the comment is treated as
alignment character? I only want to align at the *first* equals
sign, no matter what comes after:

alpha = gamma // number=first
foo = bar // another comment
one = one


Marco