Enrich: dynamically selected field

Hello, I'm wondering if there's a way to have a dynamically set query:

I've 3 fields in the country table: offset1, offset2, offset3 and I'd like to assign one of this to a variabile inside a WF, something like that:

var.offset = recipient/country/@offset2

(meaning it will refers to the value inside the offset2 field)

Then, in a Enrichment activity, I need to add data from the corresponding field, so like if I wrote directly:

[recipient/country/@offset2] but using the variabile, because the reference depends on other custom behaviors.

Is there a way inside the Select additional columns window?

I've tried to concatenate string and variable, but it didn't work.

Any idea?

thanks