LabVIEW opens it when all other VIs are closed, so you can just have a VI which is open all the time. If you don't want to see it, you can have it open a reference to itself and then set the Front Panel Window.State property to Hidden. Note that if it doesn't open a reference to itself it will be unloaded when you do this.
Another thing to note is that LV will still be in memory even though it looks like it isn't.
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