Guitar doctors say using olive oil is a very good and viable alternative for cleaning the guitar fretboard up.
Apply this much in the same way you would Lemon OIl, a very small amount as in just a thin film to the fretboard.
A caution (as with the lemon oil as well) is that using to much of this will stick to the strings and cause it to get very messy. Avoid this at all costs.
The best method I find for applying this is to get a little corner of the cloth damp with the oil, and rub it in slowly, repeating after the oil runs out, ensuring that no big globs of it are left anywhere.