Finally, there is some progress. :-)
Based on the U-Boot sources for Linksys WAG120N, I managed to create a config file for Amazon SE as follows:
0xbf800060 0x7
0xbf800010 0x0
0xbf800020 0x0
0xbf800200 0x02
0xbf800210 0x0
0xbf800230 0x0002
0xbf800220 0x30
0xbf800240 0x14c9
0xbf800280 0x36325
0xbf800290 0x81d
0xbf8002A0 0x0
0xbf800210 0x1
0xbf103010 0x20
And then used gct to convert u-boot.srec files to u-boot.asc files using the above config (amse.conf).
./gct amse.conf u-boot.srec uboot.asc
Unlike earlier attempts where I got nothing, this time after I send (paste) the u-boot.asc file into minicom, I get the UART prompt again, some sort of "reboot". This behavior is consistent, i.e., it is the same for some u-boot.asc files, while nothing happens for others. I think this is an indication that my u-boot.asc file is accepted and then rejected (sort of), which is one step ahead of not accepting at all. :-)