To date, several reversible secret sharing methods have been proposed based on absolute moment block truncation coding (AMBTC). These methods can losslessly recover the AMBTC compression codes after revealing the secret data from shadows. However, in these reported methods, one set of AMBTC compression codes, consisting of two quantification values and a bit-plane, is used to share only one secret message. In other words, the embedding capacity of the reported methods can be further improved. In order to share more secret data, we proposed a substitution and mapping method to embed more secret data into a pair of quantification values. In addition, all of the bits in the bit-plane can be used to share secret data. Experimental results showed that the embedding capacity of the proposed method is higher than that of the AMBTC-based secret sharing methods.