Trend removal options are not built into Areal Interpolation, but there are a few things you might try.
First, you may be able to remove some trend by correcting for anisotropy. It's one of the options on the covariance curve screen of the Wizard.
If that doesn't work, there is a second method that may work, but it is more statistically questionable. You may be able to represent the polygons as points and use Global or Local Polynomial interpolation to get a general trend. You can then subtract off this trend from your polygonal data and use areal interpolation on the new detrended data. After the interpolation, you can add back the trend that you removed. This methodology is hard to justify if you're using Rate (Binomial) or Event (Overdispersed Poisson) areal interpolation, but it can be reasonably justified for Average (Gaussian).
