Exactly what you want, is not possible .
The locks requests over the session profile is a acumulative information.
You have 2 ways (not a beautiful way, but, maybe work).
1) execute the "onstat -z" and refresh all statistics information (ALL statistics) and them you get how much locks requests are made over the session. (I strongly not recommend this option because if you need to monitor any other information will be an partial information).
2) execute the select over the syssesprof each time you want and calculate the difference between each one, them you will get how much locks are requested over this space of time.