SPI has been added added as a subsytem in the userapps directory tree. MATLAB can open SPI models by name and h1build should build spi models (not tested yet as there are no models to build).
You'll need to wait an hour after this post for puppet changes to propagate and log out and back into a workstation for the MATLAB path update to take effect.
The change needs to be made in two places. In CDS puppet there's an array at the top of cds-env.pp and also add to the array in /opt/rtcds/userapps/release/etc/SUBSYS.ini