Modify Query Name if the value is derived from a property?

[Jonathan-Zollinger]

Synopsis

I'm wanting to use the a property in an httpclient's url interpolation - Can I modify the query value like I can with passed args?

BackStory

My endpoint I'm pulling from has a lot of query values which dont change frequently. for instance, the store ID and product ID change often, but the values for the api key and the channel hardly change (but do seldomly change).

Current Setup

I've a getter which includes the api key by manually adding ?key=${threshr.key}. I tried doing similarly to interpolating a pojo with & for another property 'CHANNEL' but no dice (see below). Is this a supported ability? I can't find anything on supported annotations for variable interpolation

@Get("/product_summary_with_fulfillment_v1" +
        "?key=${threshr.key}" +  // (1)
        "{&targetStore*}" +
        "{&tcin}" +
        "${&threshr.CHANNEL}") // (2)
HttpResponse<ApiResponseData> productSummaryWithFulfillment(
        TargetStore targetStore,
        @Format("csv")
        Tcin... tcin);

1: this is the current solution, which definitely works!
2: interpolation which I'm failing to get to work.