What specific kind of messages are you trying to inject? Eg, you are running something in bladelogic and you want it to show up in your patrol logs?
It appears you posted your question to the wrong group. This is more of a Performance Manager question.
I happen to know that HP OVO is the same functionality as the Command Post product that BMC acquired. Command Post has evolved into what is now known as BMC Event Manager and Service Impact Manager products. Also called BEM/SIM or BEIM.
BEM specifically lets you add/modify event messages. SIM is useful for (among other things) event correlation.
If it is BEM, the command you may be looking for is msend..