You could replace CH with another two letter combination. Swedish for example uses TJ for a sound that is quite close to the English CH.

Chinese Pinyin use q for one of their two ch-like sounds -- we could do the same. Q is even more redundant than C, because not only is it identical to K, it's always followed by a U.

You could replace C occurring by itself (or where CK represents the /k/ sound) with either S or K and then replace CH with C.