Turning on sustain between variables

[jim . showalter]

If I have a simple phrase like

phrase = { a b c d e}

How do I turn sustain on and off between phrases.

The following illustrates what I want to do but of course gives a syntax error.

{
  \phrase \sustainOn \phrase \sustainOff
}

A more general question is how does one "attach"  lilypond directives/commands to variables?`

I was looking for something like a "zero-width, invisible pitch" to which I could attach the sustainOn/Off too.

Thanks,
Jim