You can write data directly to memory using the WRITEx command in the linker command file. The WRITEB command writes a byte, the WRITEH command writes two bytes, and the WRITEW command writes four bytes. You insert the data at the section's current address.
.example_data_section : { WRITEB 0x48; // 'H' WRITEB 0x69; // 'i' WRITEB 0x21; // '!' }