Not the same thing as nesting forms, but when faced with similar challenges I found the <input form="form-id" /> attribute[0] is a good solution.

The trade-off is that you have to specify it almost every single time, but it lets you group form elements that for UX purposes belong together, but for other reasons need different forms.

[0] https://developer.mozilla.org/en-US/docs/Web/HTML/Element/in...