To flash FPGA binary file (.rbt) user can use the provided C source code in the Lattice software installation directory for embedded programming.
C source code for Radiant:
<install_path>\programmer\embedded_source
Example: C:\lscc\radiant\<Radiant version>\programmer\embedded_source
For the Propel SDK (RISC-V) binary file, as of now, it is not possible to load it separately from the bitstream.