Custom TabItem on TabControl

I'd like to bind Collection of objects to TabControl, but i have to put data from those objects to CustomTabItem.

The main problem is that i don't want to create ItemSource={Binding MyList, Converter...} because during converting i'm creating time-costly objects and i don't want to load it every time i change something in binded collection and this is the way Converer is working (or i omit something) - converter gets as parameter input collection and return collection of filled TabItems or in my case, collection of CustomTabItem

How can i change style of default TabControl's TabItem on my CustomTabItem and in XAML bind my Custom User Control's properties to proper properties of object from Binded Collection?