Appending Strings in oauth_config

I'm trying to minimize the amount of parameters that I need in order to setup an app. In my Oauth configuration, I'm passing in parameters from the parameters file. My oauth_config.yml looks something like this:

client_id: {{iparam.client_id}}

client_secret: {{iparam.client_secret}}

authorize_url: {{iparam.authorize_url}}

token_url: {{iparam.token_url}}

token_type: "account"

The output of authorize url is something like https://customer.service.com/oauth/authorize?response_type=code&client_id=abcdef123guid&redirect_uri=http%3A%2F%2Foauth.freshdev.io%2Fauth%2Fcallback"

I want my authorize URL and my token URL to have a base URL that I'm already using as a parameter that I'm using in another application. 

Instead of making a separate parameter authorize_url, it would be really cool if I could do something like this.

client_id: {{iparam.client_id}}

client_secret: {{iparam.client_secret}}

authorize_url: "{{iparam.service_url}}/oauth/authorize?response_type=code&client_id={{iparam.client_id}}&redirect_uri=http%3A%2F%2Foauth.freshdev.io%2Fauth%2Fcallback"

token_url: {{iparam.token_url}}

token_type: "account"

is there a good way to accomplish this?