This is the easiest way I found:
BtnUpload.Style.Add("display", "none");
FileUploader.Style.Add("display", "none");
BtnAccept.Style.Add("display", "inherit");
BtnClear.Style.Add("display", "inherit");
I have the opposite in the Else, so it handles displaying them as well. This can go in the Page's Load or in a method to refresh the controls on the page.