The Death Note only allows the user to specify actions for the person being killed. Thus, Light would be unable to write "Bob is killed by L" and have it happen (Bob would have a heart attack). Also, the actions written in the book have to be possible for the person to do (or they die of a heart attack). So Light could not write "Bob appears on the moon and suffocates", unless Bob had a means to get to the moon before the indicated time of death.
Finally, if there were some way to pull off having someone else murder L then Light would have to know L's real name. Of course, if he had L's name then he could just write him into the Death Note directly and not deal with a middle-man murderer.
Light could try to frame L by having someone write that they were killed by L before dying. But as it is known that Light/Kira can control people's actions, and they it didn't use L's real name, law enforcement likely wouldn't give this type of evidence too much credence.