Dissolving superglue?

[Remington]

I would also use acetone. I'd take some q-tips and start working on it slowly from the sides and from inside the hole of the washer under the figure. Then I would take a thin, stable blade and use it as a level. Very slowly tho, so that the blade doesn't brake. Don't try pulling the figure. All I had ever managed with this was to bend the figure at the ankles and break the paint.

Evaporating acetone should not be that harmful if the mini is varnished. I've never had problem with this.

I hope a disclaimer in Orctrader style is not necessary. You do what you do at your own risk. 

EDIT: I would use something to pad the area I am working at. Sometimes while using the blade as a lever, the figure tends to "fly" off the washer and land on the hard table... chipped paint is evil!

[Argonor]

I think I'll try the 'twisting the washer' approach, first, then the knife if that doesn't do the trick...

Two pairs of plyers should be good for twisting...

[Remington]

Whatever you do... good luck! Let us know if it worked.