Can I pause/continue Simulink simulation from s-function?

[robotboy]

Not sure if this is possible...

I saw some documentation on get_param, but this
appears to be restricted to command line usage.
(not sure)

To be more complete... What I want to do is start,
pause, continue, and stop (end) the Simulink simulation
from external c-code.

Must I use RTW and TLC? (Hope not as this is expensive)
Can anyone offer guidance and/or point out information resources?

Thanks!