If someone on a gluten free diet, is there a way to be tested for celiac without having to consume gluten (the challenge?)

Yes: Their are blood test that Evaluate for celiac disease with certain antibodies that are usually positive in people with celiac disease

Wouldn't think so: The reason for a GFD in celiac disease is to let antibody levels fall by avoiding repeat stimulation. To trigger enough antibodies for positive screening tests, a minimum gluten challenge is necessary. A single slice of wheat bread/d for 3 wks prior to either antibody or intestinal biopsy confirmation is adequate to provide clear results. If your GFD is too effective you can have false neg tests.