I do not know any way to update a CLOB field with a long document using SQLTools. The proposed improvement is to allow to pass CLOB parameters using the &x input parameter syntax. For example, when I execute:
UPDATE document SET content=&1 WHERE doc_id=4775333087182336;
An "Input" dialog appears. But it only has a small single-line text edit control that I can not use to paste my multi-line document. It would be nice if I could tell that this parameter should be passed as CLOB and paste my long document into the multi-line text control.