I have been wondering the same (having more than 1 strain is a nice problem to have) and was thinking of using mason jars without the lids on...my large CVault is 21ltr (5.5gallons).
See below, I was able to rig something up-- this is a 4L C-Vault with a divider made out of thin cardboard from a cereal box. I cut the middle out a little so the Boveda holder can be in any position.
Separate question for those of you buying/storing larger amounts-- what are you paying for high-quality flower in bulk? I get $150/oz from my guy if buying a lb or so-- just wondering how that compares to others in NYC/East Coast?