i only know of two other ways you may be able to do this or something similar. with launcher pro plus, you can set it up to swipe up on a dock shortcut of your choosing, and it will show up to (i believe) your 20 most recent apps.
there seems to be a way to remap the hard keys if you want to get your hands dirty. this walkthrough was originally made for the hero, but the directories it mentions are similar on the x. now, here's the thing. the guide is for remapping hard keys for different app shortcuts. i don't know that the long press of home is an app. however, there is an app that shows your most recent 15 apps here:
[App] MoreRecent - Shows 15 recent apps (updated 5/18/10) - xda-developers
once you download that (if it even works on the x, looks like it was originally developed and tested on the n1), you should be able to remap the hard key to launch that app. i didn't read through the entire thread, so i can't definitively say it will work, but if you're feeling bold, make a backup and follow the instructions here:
[GUIDE] How to Remap Hardkey Actions || Custom App Launching - xda-developers
of course, you could just skip all the hard work if the above app works and just have it as a shortcut on your home screen.
good luck!