Probably the best way would be to upgrade the Absolute 1 to Absolute 3 and then sell the separate licenses for Grand and Groove Agent on eBay. You would need a dongle to send to the buyer with the license on it but perhaps you could work out a plan where they send it back after they transfer the license. It is a little bit of a complicated process but it would probably yield you the best return in investment. I had Absolute 1+, the HALion 5 upgrade ($99) and HSO ($99) and upgraded my Absolute 1+ to Absolute 3 for $199 and sold the H5 and HSO for $180 on eBay so I recouped most of the money I spent on the upgrade.
I do understand your frustration with owning those products in what feels like a dead end path destined to keep costing you more money until you bite the bullet and consolidate them into the bundle. Remember, you have plenty of time to be patient about reselling the GA and Grand licenses because, since they are upgradable, they will continue to have value to someone looking for a cheaper path to the latest version.
Which brings up an OT point…
I want to buy some of the Groove Agent Packs like Rock Essentials, Jazz Essentials, etc., but I have been hesitant because I just have this nagging suspicion that Steinberg will release a bundle with all of them included for less than my total hypothetical investment to date with little choice but to more or less write off my losses.