Messages with Variables

I am sending a message with two number values, one of which will be changing using a [line] object plugged into $f1. So the message will look like [3 $f1]. My goal is to send the values from $f1 to channel 3 in my VST. I have verified that the VST takes messages like this and it would otherwise work correctly.

In short: is there a way to send a message with changing values? Its going to a moving light so I dont want to send a different message every millisecond (maybe thats the same thing?).

Thank you!