Leaving a statue empty is like offering nothing to the buddhas and can create obstacles. Therefore, it is important to put something inside the statue, even a few mantras and some incense. This book contains instructions for properly filling and consecrating statues and stupas of any size. It includes the root text of Shälkar Melong, translated with commentary by Lama Zopa Rinpoche, which provides detailed instructions for filling larger holy objects. Also included are the Sung Drub and Rab Nä ceremonies for consecrating your holy object.
“The four dharmakaya relic mantras are the main mantras that give power to holy objects. They are what make holy objects most powerful and beneficial, and make it easy for sentient beings to purify negative karma and collect extensive merit. It is like having thousands of atomic bombs to purify the negative karma.”
145 pages, 2007 edition
For brief instructions on how to fill and bless small statues or stupas, see here
for e-reader version.