I suppose you could, but as handy as the stuff is, it can leave some miserable residue behind. Personally, i would try the hack i've seen around that involves repositioning the spring retainers, or rig it up somehow with cable ties.
The only problem I can think of by using duct tape is, by covering some of the heatsink you are allowing less area for heat to disapate. I'm not sure if it would be enough to cause any problems. I doubt it.
Several sites sell fan adapter for this reason. The fan need to force as much air by the heatsink as it can generate. The 80mm 69cfm Delta produces 15 in the pressure area. A standard 80 mm fan is lucky to push 5. That is a major differents. It is cfm & pressure. This is why that damn Detla that is mounted on my Swiftech is efficient, but whines even on low speed. The cheapest adapter that I seen is at www.cpufx.com You can even be bold! They have a 120 mm to 60 mm adapter.
I've moved to a new level.... I superglued the fan to my Voodoo 3... but than of course if I want to get it off... oh o! (don't worry I'm not that dumb, I picked a fan that will, or at least should last for a long time, and that performs to my likeings)
An alternative to superglue and duct tape is silicone glue. It is similar to silicone caulk that people use to caulk their sinks and tubs. But the glue sets a bit faster.
The reason that the glue is nice is that you can peel it off most surfaces most of the time.
I used a hardware store bought funnel and silicone glue to glue a 60x60 fan case to a 80x80 fan. That was my homemade adaptor.
What I mean by a fan case is the outside square piece of the fan with the motor and blades cut out of it. It was a cheap fan. I think the ruined fan plus funnel plus glue was less than an adaptor. (And there was no wait for shipping!)
Super glue will actually give away if you get it hot enough. I remember I superglued my tec and cold plate to my alpha the first time I set it up like the directions said. months later there was no sign of the glue any more and the tec and cold plate came right off.