1) Sell Keep the Tourer, buy an Interstate (and super-valk the trunk off if he wants onto the Tourer, along with swapping the side- and front-opening bag hardware). Prices aren't great to sell, but are great to buy these days.
2) Get a Memphis Shades or other fairing to add to the Tourer.
3) Modify the existing I/S fender struts to allow the trunk to be removed easily. Do same with a spare set and swap them with the Tourer's struts...so you can move the trunk between bikes.
4) Add the necessary wiring to both bikes to facilitate running the trunk lights and a fender-mounted taillight; source one of these and install it on the I/S' rear fender.
5) Equip the Tourer with electronics of your choice. I put the Hondaline CB, a Yaesu dual-band amateur radio transceiver and other goodies on mine. The Yaesu setup offers AM/FM BCB reception and both it and the Hondaline CB feature an Aux audio input for an MP3 unit or other sort of music player...GPS...what have you.
6) (Bonus points) Obtain and install a set of I/S radiator pods and related hardware.
My '99 Tourer has a Bat Wing (interchangeable with several other Memphis Shades products), an I/S fuel tank, trunk and radiator pods plus assorted electronics and Safety Chrome. The forks were rebuilt a couple of years ago with a set of Hyperpro springs, and though I didn't change the dampers it seems to soak up highway bumps decently. Thanks to this thread, my curiosity is now piqued about doing so...although Honda has discontinued a number of Valkyrie fork parts - including the dampers. Off the the surplus yards I go.