Can you set the output configuration at Query time?
No, there is no programmatic way (outside of what you suggested: writing a custom SSMS plug-in) to control SSMS (for the most part). Like most commands, SET commands are executed by SQL Server. The only control you could have locally is a subset of the SQLCMD commands -- :r, :setvar, :connect, and so on -- but none of those allow for configuring the UI / SSMS.

BUT, all hope might not be lost yet. Since you are giving your coworkers T-SQL templates to copy and paste and fill out, and since there are already short-cut keys to toggle between "Results to Grid" and "Results to Text", just add in a few helpful comments to direct them on how to execute the script. Something along the lines of:

/*    INSTRUCTIONS:

1) Control-Shift-M    (to fill out parameter values)
2) Control-T          (for Results To Text)
3) Control-E (or F5)  (to execute query)
4) Control-D          (for Results to Grid)
*/