um, I second putting the amp in... it'd be just as easy as wiring up the sub amp. obviously you had an amp to run the BTL unless you ran that on HU power as well.. a good reason to buy the cheapest wires you can get. you can leave them there even when you sell the car LOL...
I actually left a pioneer 8400mp and Orion P6.2 components in my last car I traded in... car was fully dynamated too, they kinda scored on the audio front...