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If you want to put the first stage in orbit, then eliminate the second stage engine, and plumb the second stage fuel into the first stage tanks. Replace the central first stage booster's bell with a wider vacuum-optimized bell. Hopefully, the weight saved by eliminating the second stage engine would make up for the reduced efficiency of that central engine, during atmospheric flight.

Easy peasy in KSP. No idea if it is possible IRL.

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Running a vacuum-optimised engine in atmosphere means the exhaust is overexpanded, which causes severe flow seperation and chaotic flow. Even small amounts of overexpansion are harmful to the nozzle; overexpansion to vacuum-type ratios is likely to cause an Rapid Unscheduled Disassembly.

I believe the main problem here is the difficulty in pumping fuel around, rocket fuel injection is not a trivial matter

source: also played lots of KSP and looked into why asparagus staging is more difficult IRL

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