You can already do that, in a way: just kill the dld. When you want to resume it again, just go over to the Library, click Incompletes, look for the file, select it and click resume (although a Pause function would indeed be less of a hassle).

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

"Raise your can of Beer on high
And seal your fate forever
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The Golden Age Of Leather"
-Blue Öyster Cult-