Ummm. yep. You just need to make a button. You can literally make an image or shape THE button by selecting it and doing 'convert to symbol' and choosing 'button'.
It's important to understand how buttons work. Inside any button symbol that you make, there are four frames, one for each 'state' of the button. Up, over, on, and hit. Whatever is on those frames is what the user will see when they invoke that state. Anyway, the point is you can have nothing on any of the states except the 'hit' state, making the button invisible (the 'hit state' defines the hotspot). This way, you have an invisible 'hotspot'.
then just put the 'get url' action on the button and you're good.