Button that looks for the current user in a table and displays the record

I suggest that you set the Key field of the Sync table  yo be the Synched Userid  it will in fact be a text field  type, but that is OK  

Then make a helper table with one Record in it. On that table make a formula URL button

URLRoot() & "db/" & [_DBID_my sync table] & "?a=dr&key=" ToText(User())


Then put that one record report with that one button on it on the Dashboard, but squish it as skinny as possible by having it take only 1/3 of the width and perhaps make the button label wordy si that it just looks like a big button to click on the Dashboard, which was your question.