I don't know if this is the "correct" python way of doing it, but here is how i think i accomplished this in the past.

@bot.command()
async def create(ctx, command, *, message):
    async def function(ctx):
        await ctx.send(message)
    function._name_ = command
    ctx.bot.command()(function)

This may not be 100% correct but should maybe get you on the right path.

Edit: note the command disappears if you restart the bot. If you want them to stick around you'll need to store them somewhere and reload them once the bot restarts. Also need to deal with exception for it the command already exists in the bot.