Use DNA to clone John Lennon body/brain. Body would be discarded after process. Brain may be kept for further mapping/storage.
Use neural mapping technologies to create a model of John Lennon's brain. Brain would be stimulated to approximate events in his life until maturity.
- Events could be changed to create, "alternate universe" John Lennons.
Use neural map to create simulated reconstruction of John Lennon's brain inside computer. Computer will need significant computing potential. Cluster arrays may be useful.
Use hologram technologies used for 2Pac to reconstruct visual copy of John Lennon's body.
Use sophisticated computer algorithms as control for hologram. Seed data would be provided for by previously mentioned reconstruction of John Lennon's brain.
Set up installations throughout major cities where one can interface with the LENNONBRAIN at will.
All you need is love.