Cache MultiScaleTileSource in Isolated Storage

I trying develop a custom map application.

I'm using MultiScaleTileSource class and I want to cache data in the local Isolated Storage.

If I will put download function into GetTileLayers method it will hold th开发者_开发问答e main thread of the application.

I think it would be great to redefine the Httprequest method for MultiScaleTileSource, but how?

May be there are any other approach?

Thank you in advance!