You say you want to invoke a web-service. Have you looked at the service-provider's WSDL? Netbeans will automatically create stub-code for you just based on the WSDL; you only need to fill out your code within that stub and you have yourself what you need.
If, on the other hand, you meant that you need to create a web-service which must sign some content using two different private-keys using XMLSignature (DSIG), may I suggest you ask the group that creates the reference DSIG library? firstname.lastname@example.org
There are many other ways to solve this problem, but if the DSIG standard has a schema definition/use-case for this, it will surely have been implemented by the developers on the mailing list I've provided.