Arrow at end of slur (like in Carter's 2nd string quartet)

[Mike Solomon]

Hey lilypond-users,
    I am looking to use a slur with an arrow at the end like Carter uses in
his second string quartet.  The slur behaves like a regular slur, save the
fact that at one of the two ends there is an arrow.  He uses this to
indicate slight accel/rit within a fixed duration (a rubato of sorts, but
more prescribed and unidirectional).  Before I undertake the work of
overloading the stencil object for Slur, I was hoping that there was an easy
tweak to make this happen.

Many thanks!
~Mike