I'm assuming you've moved on from this problem, but here's something that might help. Only the core of Tk is accessible by default, but it seems that you can get at the rest of it with a little effort. I spent all day trying to write my own Tkx tooltip functionality, and after failing to successfully debug mysterious memory leaks I stumbled upon a way to use Tk's tooltips.

Tkx::package_require('tooltip');
Tkx::namespace_import("::tooltip::tooltip");

Tkx::tooltip($widget, "Some text.");
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Note how Tkx::tooltip won't work without the require and import lines. Perhaps you can get at Tk's drag and drop functionality in a similar manner. Good luck.