CR 8.5 and below can't use them in formulas, in fact you're limited to fields of 254 or less.
You might get around this by creating a SQL Expression in Crystal which parses it down to 254 characters, such as:
substr(table.field,1,254)
A wild guess at the syntax because you've posted nothing technical, such as:
Crystal version
Database/connectivity used
Example data
Expected output
In other words, your post doesn't ask for anything more than confirmation of what you already know, that you can't use it.
Why not post what you have, and what you need?
-k