This will most likely work, although it sounds a bit bodgy.
A smear of grease on the taper then wrap in two or three layers of aluminium foil with Loctite 641 between the layers and inside the degreased crank arm.
Fit as normal, making sure the crank arm goes over the foil and doesn't scrunch it up. A drop of 263 on the bolt and torque it up. Leave it a few hours and then ride and re-check for tightness.
The foil gets displaced from the areas that are making perfect contact and fills in those that aren't, bonded into place by the 641.