Working with BLOBS

Hi - PL/SQL Oracle 8i (8.1.7)

We have a document stored in a BLOB. We know this is an RTF (rich text format) and it contains 'placeholders' (e.g. [last_name] which we then wish to substitute with the person's name).

So we read the BLOB into a PL/SQL block - what is the most efficient/easiest way of performing our string replacements?

If it were in a varchar2, we could simply say

  l_doc := replace(l_doc,'[last_name]',l_last_name);

Is there an equivalent with BLOBS? Or do I need to read it in chunks into a varchar2, process it and then reassemble it as a new BLOB?

Thanks for any pointeres here....

-- 

jeremy