Here is an idea.
Buy some dozens of large canvases and some water paints, brushes etc.
Throw some paint on the canvas in any random way you want, or try and paint a tree or water or a penguin it really doesn't matter. But the more useless and tasteless the better (it's called abstract modern art FYI).
Print some flyers, create some media ads (sales pitch) presenting your "art" as the greatest thing since sliced bread. Rent a modern art gallery for a week or two and put the "paintings" in there.
Now have a trusted (or imaginary) client/collaborator "buy" your "art" with your own bitcoins for astronomically overvalued price.
There. You now have legit source of income for those bitcoins; pay the tax and live happily everafter.
I mean, modern art galleries are the ultimate money laundry scheme, aren't they? They have to be. And so are cryptocurrencies.