Yes you can just bump up the contrast of an image to make it appear like an hdr, but you will not get the added effect of it actually casting light into the scene, so you'll only see the effect if you have lots of reflected objects.

Here's an action I made for photoshop that will give you a "bloom" effect on highlights:
Save it to disk and in photoshop, find the actions pane, click the little arrow in the upper left of it, and select "load actions." Then broswe for the file and load it. It will appear in the list under "bloom fx." Select the action and press play :)

Here is an example scene including a "fake" hdr reflection dome:

Message edited on: 12/11/2005 12:57