Assembly Code Multiplication

[DoomSlice]

Anyone know how to do an efficient Assembly Code multiplication of 2 15 bit numbers into a 32 bit register using the following operations:

nand rA rB dest
add rA rB dest
beq rA rB offset (branch to offset or label if rA = rB)
halt

I need to simulate bit shifting by using add and somehow use nand to figure out the product of the two by using some combination of nands.