assuming you have a commutative encryption operations (like XOR)  where  ((pt+E1)+E2)-E1 = (pt+E2)

then

person A                      person B
OTP char a                    OTP char b
message pt
pt+a            ------->        pt+a
pt+a+b          <--------       pt+a+b
pt+a+b-a
pt+b          -------->         pt+b
                                pt+b-b
                               message pt