Calling infoPath form code from a Web Service to populate a drop down list

Using a web service solution to retrieve SQL data I'm wanting to return the list of values that I've collected and call the InfoPath form code to populate the drop down options. How do I call the form code from the web service?

I take it it's quite alike to calling the web service from the form code eg.

ServiceTitle.Service svc = new ServiceTitle.Service();

//assign field values to oFieldInformation

svc.WriteToSharePointList(oFieldInformation); //web service procedure

Let me know if theres any more details required