Ummm, no, that doesn't help me understand it unless you mean that you want to place spaces between the characters to keep the field at a constant length.
You cannot conditionally stretch or shrink tohe field itself, however you can have several of them laying over the top of each other and conditionally suppress, as in:
Field 1 suppression:
len(trim({table.field})) <= 3
Field 2 suppression:
len(trim({table.field})) > 3
and
len(trim({table.field})) <= 6
Field 3 suppression:
len(trim({table.field})) > 6
and
len(trim({table.field})) <= 9
...etc...
Try stating specifically what it is that you want, keeping in mind that fields won't stretch, however they can grow (will drop down to the next line), or you can change fonts or have multiple fields overlapping, or perhaps you want to insert spaces between the actual characters.
-k