Is is possible to split Qsys conduits

I think you can define a custom component based on the original device.

First of all, create wrapper code which implements the division of the standard_logic_vector using the VHDL code above, while it simply connects all the other ports pin to pin.

Then in the component _hw.tcl file you expose internal signals with lines like this:

add_interface_port conduit_end <internal_signal> export Output 1

I'm almost sure you can do the job with a simple tcl script, without the wrapper, but I'm not very expert on this subject.