Hai guise, this wasn´t my own original idea, I read somewhere how someone made it work with an Electribe and Volca and I saw no reason why it shouldn´t work with an SP.
It does!
I have an SP-404SX and a Volca Bass and it works good, it´s a workaround and has downsides but it´s still fu**ing genius IMO.

So you route the Volca´s sync out to your samplers input and record the sync-click the Volca is sending out as audio. Pan it all the way to right for example and leave silence in the left channel. All the other samples (which you use for the actual music itself) have to be vice versa, stereo, with nothing in the right channel.
Put the sync-click sample on loop and feed the right channel to Volca´s sync-in. Volca now follows the tempo of your SP! If you have a pattern playing and you change tempo the volca follows.. magic.
Everything else goes out through the left channel into your mixer/amp/speakers...

The downside is that now you are forced to have every sample in stereo and your polyphony is 5 (while your sound is mono), since 1 sample is always occupied by the sync-click.