I was right...

... for the wrong reasons. In fact, you cannot use storage objects to set BLOB command parameters. I found that the usual mechanism does not work because:

1. When retrieving command parameter information through GetParameterInfo, you don't get the DBPARAMFLAGS_ISLONG bit set for BLOBs;
2. Binding a BLOB parameter through a storage object causes the Execute method to fail reporting a DBSTATUS_E_CANTCONVERTVALUE on the BLOB column.

So I had to revert to the old code that buffers the parameter values in a buffer and forces a rebind when the new set of parameters is larger than the old parameter buffer (used by the accessor). Now that I got this straight, it's time to finish the new demo that inserts BLOBs using a parametrized INSERT command. Please stay tuned for the next post.