Thanks to another post I made, I have solved / had this problem solved for me. I created a slide object that holds an image/file and a caption as properties. From the Slideshow widget code behind, I create a repeater and get the HTML output from transform for the objects placed in the directory specified in the slideshow widget. Here's my code behind for reference for anyone else maybe coming across this later.
protected void Page_Load(object sender, EventArgs e)
{
slide_script_wrapper.InnerHtml = string.Format("<script>{0}</script>", AddSlides());
}
protected string AddSlides()
{
Page pageHolder = new Page();
CMSRepeater repeater = (CMSRepeater)pageHolder.LoadControl(typeof(CMSRepeater), null);
//Set Parameters.
repeater.ClassNames = "custom_1023.slideshow_slide";
repeater.Path = GetValue("ImageDirectory").ToString();
repeater.TransformationName = "custom_1023.slideshow_slide.Default";
pageHolder.Controls.Add(repeater);
StringWriter output = new StringWriter();
HttpContext.Current.Server.Execute(pageHolder, output, false);
return output.ToString();
}