You can buy a varus wedge for about $2 at a good shoe store.

Take the insole out of your shoe. The backing of the wedge peels off, and you stick it butted up to the inside edge in the toe-box directly to the shoe. (wide part against the big-toe side, tapering toward the 3rd toe.) Then put the insole back into the shoe.

Any shoe store that sells varus wedges should be able to tell you what thickness you need in your cycling shoes and will probably put them into your shoes for you if you ask.