What a cool idea. A couple things you could consider doing, loosely based on things I've been experimenting with (though never with anything as delicate.)
The esters in those are probably very very volatile so tossing them in the boil is going to drive everything away. SO to capture the essence your going to have to try things like infusions and like dry hopping. Using them in ways that won't drive off those delicate aromas and flavors.
You could try infusing vodka, or grain alcohol with a lot of blossoms, and add them or just the extraction to the beer post fermentation like in secondary.
Another thing would be to steep them in your priming solution and strain them out and add that to your bottling bucket at bottling time. I've been experimenting with infusing my priming sugar boils with all manner of things, like spices, ginger, herbs, even chillies. Basically once you hit the boil for your priming solution turn off the flame and dump them in, AND put a lid on the pan to trap everything in, including the distillate at the top of the lid. (Hmmm, that's another thought. Creating and infused distilled water and suing that.Basically doing something similar to how ALton Brown makes distilled smoke on good eats (
http://www.thesmokering.com/forum/viewtopic.php?p=31533&sid=07d4f25fab7911c06206898044a6c0ff)
In fact I wonder if you could distill enough orange blossom water that way for the two cups of water you need to prime with.?
Another option might be to dry hop with them.
Also, you could try infuse dry sugar with them and adding that to something..like ssecondary or your priming solution.... I've infused sugar with ginger by peeling whole roots and sticking them in a jar and filling the jar with sugar and letting it sit in the fridge form months, then removing the ginger and letting the sugar dry out and using that on cookies and stuff. You might want to try that.
I also wonder how mashing them would work...but I wonder if the 150 heat would destroy the oils..but it might be perfect.
All these things though probably require a ton of blossoms to get enough of an impact.
But I think it might be cool to try.
Obviously you'd probably need a very low grav beer like a kolsh or a pale ale to use them in that wouldn't over shadow the blossom aroma or flavor itself.
Good luck
