Use the src-mac, enabled ip
http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/1219ea1/3550scg/swethchl.htm#xtocid15
src-mac.
When src-mac is used, load distribution based on the source and destination IP address is also enabled. For all IP traffic being routed, the switch chooses a port for transmission based on the source and destination IP address. Packets between two IP hosts always use the same port for packet transmission, but packets between any other pair of hosts might use a different transmission port.