I got SO tired of mixing gas to get a higher octane, I rebuilt the motor. Couldn't be happier. OK, a fairly radical approach.
But IF I had an all ready great motor and wanted to 'simply' reduce the compression ratio to a reasonable level, I'd go with THICK head gaskets to increase the combustion chamber size and thus lower the c.r.
No matter how you cut it, 'mixing gas' gets old, quickly.