Something

// ==UserScript==
// @name           Character Selection
// @namespace      http://ikebowen.com
// @description    Manual hackish thing for selecting a Jetman character without "earning" it.
// @include        http://apps.facebook.com/playjetman/*
// ==/UserScript==

function setNewJetmanCharacter() {

	var divs = document.getElementsByTagName("div");
	for ( var i=0;i<divs.length;i++ ) {
		if ( divs[i].id.search("4243149646_fbswf_") != -1 ) {
			divid = divs[i].id;
		}
	}

	if ( document.embeds[0] ) {
		var newchar = prompt("Give a character ID to use (take a guess based on the order of characters presented by Jetman in the actual selection screen):","(integer only)");
		eval("unsafeWindow."+document.embeds[0].id+".addVariable('character', '"+newchar+"');");
		eval("unsafeWindow."+document.embeds[0].id+".write('"+divid+"');");
	}

return false;
}

imgs = document.getElementsByTagName("img");
for ( var i=0;i<imgs.length;i++ ) {
	if ( imgs[i].src.search("choose_character.png") != -1 ) {
		imgobj = imgs[i];
	}
}

imgobj.parentNode.attributes[2].nodeValue="";
imgobj.parentNode.attributes[1].nodeValue="Javascript: void(0); return false;";
imgobj.parentNode.addEventListener("click", function(e) { setNewJetmanCharacter(); return false; }
, false);