How does Claudius manipulate Rosencrantz and Guildenstern in the play?

In addition to hiring Rosencrantz and Guildenstern to help
him with Hamlet's depression, Claudius perhaps has planted the seed that Hamlet's
melancholy has resulted from the fact that his ambition to inherit the throne has been
thwarted by Claudius and Gertrude's marriage.  Notice in Act 2 how often Rosencrantz and
Guildenstern use the word "ambition" in their questioning of Hamlet.  It seems here
that  Claudius has commissioned Rosencrantz and Guildenstern not only to find out what
is wrong with Hamlet, but also to determine if Hamlet had past ambitions for the throne,
and if he is still harboring those same ambitions. Claudius obviously views Hamlet as a
true threat, and he is using the two spies in an attempt to find out Hamlet's
motivation.

 Later, Claudius uses Rosencrantz and
Guildenstern to escort Hamlet to England where Claudius plans for him to be executed. 
Of course, this plan does not work, but we are not sure of Rosencrantz and
Guildenstern's knowledge of this plan.  Perhaps they are innocent of the orders they are
carrying.  Perhaps not.  Hamlet likens them to "sponges" or "knee-crooking"
knaves--sychophants that will do whatever they are told to promote their standing with
the king.