Use sp_drv_text_setdata which accesses the Transact-SQL function setadata.
sp_drv_text_setdata locator, offset, new_data, data_length
locator – a text_locator that references the text column to insert into.
offset – an integer specifying the position from which to start writing the new content.
new_data – varchar or text data to insert.
data_length – an integer containing the number of characters written.
None.
