Unlike other workarounds, this one doesn't use any of Sampler's usual mod sources (LFOs, MOD ENV etc). Instead, the Sample Offset parameter is controlled by the Velocity and Arpeggiator devices.
The crapily-monikered 'VeloStretch' comes in 2 versions, both available in the .zip link below. 'VeloStretch DR' is a drum rack that's designed to be used as a Slicing preset (drop it in Library/Defaults/Slicing), and 'VeloStretch' is the Sampler instrument rack.
>>> Sampler VeloStretch Racks <<<
