Here's an idea that might work like Bailey's pipettes. I found that some eye drops have measured doses stored in miniature vials/pipettes with a neat little replaceable caps. The plastic looks to be the same stuff as the pipettes and so probably has the same permeability for the lemony smell to get out. The blurry picture below is of a Cellufresh eye lubricant drops vial. A box comes with 30 of the little vials and each vial originally contains about 1 cc of basically saline solution, so nothing nasty to bees. The only problem I forsee is that once the initial seal is broken, they are not longer air-tight, but that shouldn't be a problem if they are placed pointy end up. A thumb tack through the flat end would be perfect to secure one in your swarm trap. I will try a few when spring arrives here.