If you know the channel and time of the show, you can start by trying to record any program on any channel, and choose "Record by time" option. Then you change the channel and start time, and duration.
On the other hand, if you don't know the channel and time, but know the name of the show, you can use Subscribe option. Again you start with any program on any channel, and then modify the subscription parameters. For example, if you know the channel, you can specify it, but if you don't, you choose "All channels". If you know the day of week and time, you can specify that too, otherwise choose "All showings". This is like casting a wide net, and its success will depend on the accuracy of your search phrases and other parameters you specify.
I know it is a little non-intuitive, but adding a new button would just duplicate the same functionality.