Running skill function before simulation to prevent its start

I'd like to set up my environment to run a skill function just before a simulation starts to check system load. If the load is too high, it will display a message and prevent the simulation from running. I need to support both ADE-L and ADE-XL. What's the best way to do this?

From what I've found in the documentation, I can add a pre-simulation callback in ADE-XL using the axl* functions and signals/triggers. However, it does not appear that the callback can prevent the simulation from running.

For ADE-L, I've not been able to find a similar pre-sim callback. I could either overwrite all of the toolbar buttons and menu items, or overwrite the run functions. It seems that the UI elements are all re-generated and the callbacks for them changed every time the simulator changes, which poses a problem.

I can overwrite all of the run simulation functions, but I'd have to do so for every simulator (assuming they don't get re-defined on simulator changes).