In general, it would be better to keep your starter at 1.020 than to boost it up to 1.040 with corn sugar. This is because the yeast have an easier time metabolizing the corn sugar and will consume it preferentially to the malt sugars. This is supposed to make the yeast because lazy so that they stop working hard enough to consume the malt sugars. I can't tell you the chemical or biological reason for this, but enough brewing experts that I trust have said this that I believe it. So by adding the corn sugar, you've created lazy yeast which defeats the purpose of your starter.
Currently On Draft: Bamberger Rauch Dunkel, Belgian Blond, Pilsener Urquell clone, Smoked Porter
Bottled: Concord Pyment, Mi'Apa Sparkling Mead, Chimay Blue, Old Simcoe American Barleywine, Old Cantankerous
Fermenting and Conditioning: Pseudo-Decoction Munich Dunkel, Left Hook Bitter
Recently Kicked Kegs: Fresh Hop Pale Ale, Citra Rye IPA
On Deck: Old Rasputin, Northstar IPA, Ur-bock Dunkel