If you're using the free version of ESXi and specifically U4, then no there is no other supported method of enabling SNMP or performing any other write operations. As you've already verified, going into the unsupported SSH busybox console is one method or you can use the VI Client to enable SNMP.
VMware vExpert 2009
VMware ESX/ESXi scripts and resources at: http://engineering.ucsb.edu/~duonglt/vmware/
what is the console command to edit this file?
to edit, type 'i'
to save your file, type ': x'
Now unfortunately, I need the MIBs.
Would you happen to know where they are?