使用modal true打开jquery对话框后启用按钮

I want to enable a button after that i have opened a jquery dialog with option modal set to true.The button obviously is outside the dialog. I already know that this seems to be a strange request but i need this behaviour because I have a form in the dialog so after click on the button to submit the data I have to append the dialog at the end of the form and then click agin on the button that now is outside of the dialog. I want to enable a button after that i have ope