No, this is with all switches off, the only way to do it is to delete debug.log while client is running.
EDIT: When its deleted while running, it will stop writing log data.
Is there a way to delete the debug.log on Windows when the file is being locked while the wallet is running?
Google "Windows unlocker". I don't know which program is free/best/easiest, but any one should do the trick.
Tried that but they all kill the process associated with the file. In this case the wallet itself. When you start up the wallet again it recreates the debug.log and starts filling it up again. Need to figure out a way to delete the file without killing the wallet process while deleting.
I found a way to open the wallet without writing to the debug.log file!

Just add this argument to the target of the biblepay-qt:
-printtoconsole
Send trace/debug info to console instead of debug.log file
But actually it will not send it to console either. And if you delete debug.log before starting the wallet, you will see that debug.log will not even be created at all.
So this seems to alleviate the disk I/O load for now.