Dynamically using same method in multiple webservice references?

In c# .Net Framework 4.5 (Visual Studio Ultimate 2012, Version 11.0.61219.00 Update 5), I'm trying to define a service variable at runtime for which webservice to use. Each webservice (there are many) are all defined the same except for the endpoint url but the credentials will not cross over to authenticate. The below condition is menial to simplify the issue at hand. The following code gives the error: Cannot implicitly convert type 'WebService2.Service' to 'WebService1.Service'.

What I've tried: calling functions to return the proper service but the parameters or assignment all require a specific type.

var service = new WebService1.Service();
service = new WebService2.Service();

I want to be able to use the variable 'service' in the rest of the program without having to duplicate code everywhere for using the many webservice references.