Webservice Security and Windows Certificates

I want to sign webservice requests using Apache CXF and WSS4J. As far as I know, I would need a JKS store containing the certificate I want to use for signing. There's the requirement to be able to use a X.509 certificate from the Windows certificate store. The certificate shall be read from the store at the time of signing the webservice request. I know how to access the store and get the certificate. But how can I use it for signing instead of the certificate from my own JKS store?