My FT-450D has a first IF of 67.899 MHz which is within the tuning range of the DVB-T dongle. I tapped off the output of the first mixer with a small capacitor and snuck a coax through the rear grille. I spliced the coax into the cable going to the DBV-T, plugged the DVB-T into the computer and the hardware part is done.
Using HDSDR, I now have a 2.4-MHz-wide panoramic display. HDSDR has a setting where you can enter the IF and any additional offset; in my case I use 67923000 Hz with a 24000 Hz offset, and I swap I & Q to reverse the frequency display. After trimming the frequency correction the display tracks the VFO perfectly. (Note that the display has zero at the center; not the actual receive frequency).
I can play any signal that is within the 2.4 MHz bandwidth through the computer by simply clicking on the display. By tuning the DVB-T separately, I can go a few MHz above and below the IF and still receive reasonably well.
This should work with any radio that has a high first IF. The trick is to avoid bandpass circuits. In the FT-450D, there is a low-Q tank circuit directly in parallel with the mixer output so there is some attenuation 20kHz either side of the center, but this seems to have little impact. The roofing filter immediately follows and any point after that would have a severely restricted bandwidth.
There was another similar posting earlier, but that was about using the DVB-T and an upconverter as a parallel receiver.