I just started a few days ago so I cannot give you a good, nor the best answer, but Hypothetically speaking I believe this will work.
In flash say you create a button, and in cryengine you press the button. In flash you would have a function
button1.onPress = function()
This is the only way I am aware of at the moment, so you can use it till you find a better way.
You must setup an xml file in the UIElements folder so it can recognize your UI, find richman1 tutorials if you need to see how.
Then make a flowgraph node under ui -> yourflash -> dothings_1
And whenever the button is pressed, you link up whatever you want to the node.
Hopefully that can give you a start, that's the best i have got right now
"Pain is only weakness leaving the body"