In order to upgrade to a microprocessor with a floating point unit (FPU), it is necessary to remove the existing microprocessor from its socket and replace it with a 68040 microprocessorof similar speed. These models have no specific FPU socket on the logic board, thus the requirement to replace the CPU chip.
Such an upgrade would not come from Apple. Apple has no plans to market an FPU upgrade, nor does Apple officially support this configuration.