Update sandbox webpart custom property in SharePoint 2010

I have a SharePoint 2010 sandbox solution with a webpart (with Silverlight). My webpart has a custom (string) property. It seems it is not an easy task to update this property remotely. I have been using WebPartPages.asmx web serivce of SharePoint but its methods for load/update of webparts don't work in sandbox solutions, because the webpart is wrapped in another one, called SPUserCodeWebPart. So, is there a way to bypass this restriction?

I have noticed, that if I expose the property (WebBrowsabl开发者_JS百科e attribute = true) I can modify it in the toolpane on the left. However, I don't like this way because I use this property as a property bag (XML with my custom settings).

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Even if you get this working, you will hit the permissions problem (only users that can edit the webpart can edit the property, if you mark it as personalizable all users will have their own version of the property), so you have to move to a List storage for this one.