If he wants a higher yearly average, he has to forgo the big signing bonus. If he wants more guaranteed money then he has to take less per year for a longer term.
Either way, they can't use Murray's contract to create room for other guys by using a large signing bonus or restructuring it every year. If they can get him for a 5m cap hit and little Dead Money every year, making it easier to cut him, then that would be OK.
5 yr/30m 5m signing bonus 8m guaranteed
Year-------Sal--------SB------Cap hit
2015-------3m--------1m-----4m
2016-------4m--------1m-----5m
2017-------5m--------1m-----6m
2018-------6m--------1m-----7m
2019-------7m--------1m-----8m