Multiple TACACS+ servers with different keys

Have you ever tried to add more than one TACACS+ server??? When I tried I was forced to use same authentication key for them (it could be possible security issue)

tacacs-server host 192.168.1.100
tacacs-server host 192.168.1.101
tacacs-server key secretkey

Its difference from RADIUS command where you can specify key after IP address

radius-server host 192.168.1.100 key secretkey1
radius-server host 192.168.1.101 key secretkey2

Now I found workaround how to do same for TACACS+ it can be done with server-private command under aaa group server
NOTE this command was introduced to IOS 12.3(7)T so it doesn’t apply to current blueprint version

aaa group server tacacs+ my-servers
server-private 192.168.1.100 key secretkey1
server-private 192.168.1.100 key secretkey2