How can I use custom loadouts during test drives for Golden Eagle/pack vehicles?

While test-driving the Su-39 in my hangar, I noticed that there’s no preset option that includes the Kopyo-25 radar pod along with the Kh-29TE (or any other air-to-ground missile). I also couldn’t find any option to customize the loadout. Could someone kindly tell me where this option is located?

If it really isn’t possible to select a custom loadout during a test drive, then how am I supposed to evaluate the Su-39’s ground-attack capabilities using the Kopyo-25 radar in air-to-ground mode before deciding whether to purchase it?

You can’t. You have to own a vehicle in order to make custom loadouts.

thank you