Here are a couple of options, I'm not sure which is the best.
1. create a CLR stored proc and call the proc from a T-SQL job step.
2. create a ssis package that has a script task. Call the service from the script task.
3. generate a proxy for the WCF service, and call it using a powershell job step. I know this works in regular powershell, but it might not work in sqlps.
Option 2 is probably the easiest.
good luck.