[Steev42]

Well, I did it for myself, so I may as well share.

  <thing id="pExpRet" name="Expeditious Retreat" description="Your speed increases by 30 ft." compset="InPlay">
    <fieldval field="pMinimum" value="30"/>
    <fieldval field="pMaximum" value="30"/>
    <fieldval field="pDuration" value="1 minute/level (D)"/>
    <tag group="Helper" tag="AdjSpell"/>
    <tag group="Helper" tag="NoIncr"/>
    <tag group="Helper" tag="AdjNoPlus"/>
    <eval phase="First" priority="1000"><![CDATA[
      ~ If we're not enabled, get out now
      doneif (field[pIsOn].value = 0)

      ~ Add to speed
      hero.child[Speed].field[Bonus].value += 30]]></eval>
    </thing>