Calling Javascript with Flash

Question

If I call a JavaScript function from flash like so:

ExternalInterface.call("main");

This is all fine and good, but I want my scope to be a particular prototype, is there any way I can do something like:

ExternalInterface.call("someObj.main()");

So that the keyword this points to someObj? I'm not against somehow passing it as an argument in, I just need to get it to work.