[plt-scheme] on-execute method in drscheme:language:language<%>

I am working on a language-level for DrScheme, and I need to do some  
computation when 'Run' is clicked (before allowing the user to  
interact with functions appearing in the definitions window).

I thought that the right method to override would be on-execute in  
drscheme:language:language<%>, but that method gets invoked more  
often that I want.  In addition to being invoked upon clicking 'Run',  
it also is invoked upon opening a file in DrScheme (when my language  
has already been selected).

Is there another method that only gets invoked upon clicking 'Run'?   
Alternatively, is there a way to determine, within the body of on- 
execute, whether the invocation was triggered by the 'Run' button?

(BTW, I am using version 349.100-svn15jun2006.)

thanks!
-Dale