The simplest solution is to add the form to the DOM by yourself in the before block and then delete it in the after block:
describe(function(){
var form;
beforeEach(function(){
form = $('<form>');
$(document.body).append(form);
});
it('your test', function(){
})
afterEach(function(){
form.remove();
form = null;
});
});
Also writing your sandbox helper isn't that hard:
function sandbox(html){
var el;
beforeEach(function(){
el = $(html);
$(document.body).append(el);
});
afterEach(function(){
el.remove();
el = null;
});