FFF, I use real orange juice (not concentrate), and thicken it with some arrowroot if I have to, when it's called for in
small amounts like this recipe. The only thing is that you then have a bunch of OJ in the house. Thankfully, my DH drinks it lickety-split so I'm not tempted.
The other suggestions are good, though. I'd think the SF orange marmalade idea would be very yummy!

You could also try SF orange syrup.