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I guess there's not much choice here. The best I could suggest is a smear of silicone grease. Just enough on one face of the olive to hold it in the female end of the stainless line.
There are different types of silicone grease strangely enough. The thickest viscosity I've used is high vacuum silicone grease. I've also recently picked up a 1 ounce container of o-ring silicone grease and it's also really thick.
I wouldn't use bearing grease or the like for fear of contamination of the brake fluid but on the same breath, I don't know for sure about the silicone reaction with brake fluid. I do know that lots of brake caliper assembles use the silicone grease to install the u cups or quad seals before the pistons are installed, so that's why I suggest the silicone grease here to hold that olive while you assemble.
Hope this helps,
KB

Thanks good idea, I could only think of inserting a piece of safety wire (type used for sucuring bolts) starting the flare nut and then pulling the wire through the line I will check into silicone grease for sure.