Realize that in a keggle, a large potion of the built up heat that you're trying to dissipate is stored in the stainless keg itself. They've got fairly thick sides and bottoms. If you're going to avoid an immersion chiller and have a reasonable cooling time, you need to cool the keg (spray with garden hose, but risks contamination) or remove the fluid from it before chilling.
Lets try to think up some crazy ways to do this...
You don't say how big your batches are, but you can fit a gallon of wort into five 1-quart mason jars, or even a tiny bit more if you really squeeze it. A case of twelve will set you back $10 at Walmart, plus tax, and that includes the lids and rings to seal them up. Two cases -- $20 worth -- would hold a 5-gallon post-boil volume. Four cases -- $40 worth -- would hold a 10 gallon post-boil volume. Put the lid on gentle, then tighten the ring finger tight (just enough to hold the lid tight enough to not leak liquid when shaken), toss them in a fridge or freezer or both, and you're there. The cooling will create a vacuum that will suck the lids down for a nice temporary seal. If you're worried about shocking the glass, you could pre-warm the jars to 150F in the oven. Better yet, you could bake them at 250F for 30 minutes to sterilize, then cool to 150F.
Or, transfer the wort out of the keggle, pouring it from as high as you can while still being able to cool the stream, into your old kettle. That'll knock off 20 degrees or so. Into the pre-heated mason jars and then into a warm water bath. Then a cool water bath. Then an ice water bath. The increased surface area will work to your advantage here. Or, into the fridge until below 100F, then straight into a cooler full of ice water.
Mason jars are super useful in a brewery (hops storage, canned starter, canned priming sugar, specialty grain storage, adjust or finings storage, etc etc), so it's not like they become useless once you can afford to get that IC eventually.
Or stir like hell with a power drill. I use a helical paint mixer in a power drill to circulate large amounts of wort around my IC. My paint mixer was $7 at Home Depot. -link-
Be sure to boil the fins once before using in wort. As a bonus, you're aerating at the same time.
Do any of these whacky ideas help?