New Blog Template Plugin on Custom Signup

I have a highly customized signup form using a handful of WPMU plugins (Pro Sites as well) and I'm trying to get the New Blog Templates options to be selectable on my custom signup form.

I already have the menu / dropdown for the New Blog Templates plugin displaying on my signup form, so that's going well. However, I've spent alot of time looking over the source and it doesn't look like there is a clean separate of roles for the public methods of the functions. Lots of action hooks embedded that I can't use since I'm not on the default WP signup form. I have inspected my $_POST and it is successfully transmitting $_POST['blog_template'] with it's ID, however, new blogs are successfully created but are not receiving the chosen blog template. I've included all of the plugin's files (just to be safe) and I'm instantiating a new blog_templates() class but it seems like the constructor (which is long and a bit tough to follow) is probably not doing what I want it to. I've also tried to call $blog_templates->set_blog_defaults directly with no success. @Vadislav's answer over here is helpful (https://premium.wpmudev.org/forums/topic/remote-blog-creation-and-blog-templates) but I'm calling wpmu_activate_signup() and having trouble hooking into the blog_templates-blog_template filter at the right time.