you cant WATCH who is buying..
you could call dealers to get a read on trade flows but they would likely tell you to call another desk (if they didnt know you). traders usually distribute color throughout the day. depends on who you read and the accounts they work. besides that, keep your spreadsheet up to date and watch yield spreads change throughout the session....
you could do this.
youll need live pricing to stay ahead of lenders btw.......................