Don't know any method to specifically pause based on a full-screen application, but you can use the <exclusive_app> method. To use this, in your cc_config.xml (located in your BOINC data-directory, if not present just make it) and the file should look something like this:

<cc_config>
<options>
<exclusive_app>wmplayer.exe</exclusive_app>
</options>
<log_flags>
</log_flags>
</cc_config>

If you've got more than one application you'll want to stop BOINC-crunching for, just add these on new lines, each between their own <exclusive_app> </exclusive_app>-tags.

Note, depending on how old your BOINC-client is, it's possible the application-name is CaseSensitiVe, don't remember in which client-version it was made case-insensitive under windows...

After editing your cc_config.xml with one or more applications, in advanced view, choose to "Read config file" (under advanced menu-choise) and verify if it's working for the application(s) you've added. Note, for this to work, the "Activity" must be "Based on preferences".


BTW, for anyone running other projects besides WCG and is using a GPU, there's also a separate <exclusive_gpu_app>-tag that can be used to stop GPU-crunching.