Is this possible? If so, what is the command?
I didn't try it but the "normal" way doesn't work?
./tezos-client set delegate for "my_implicit" to "delegate"
Since Babylon, there is no need to "flag" an implicit account as "delegatable"
"In protocol 005, tz accounts which are not registered as delegate can be delegated towards a tz account registered as delegate"
Just the other way around is still needed.