Sure, this can be fairly simple to do. I have never used the default lookup feature, I always code my own, I find it default too limiting.
The basics are create a form (I like to make the form a dialog box and disable the title bar properties) for the lookup table and include the desired fields. The form should contain an "Ok" and a "Cancel" button using formReturn("Ok") and formReturn("Cancel"), doesn't have to be ok and cancel, can be anything.
On the main form trap the keyPhysical event for the space key and the control key to duplicate the default key combination. You could also use a button or any other key combination.
Open the lookup form from the main form and issue a wait() if the lookup form returns "Ok" grab the values from the lookup form and insert them into the main form. This is easy to do using the field names if all the fields you need are displayed on the lookup form. If all the fields are not displayed you can still make things work it just takes a little more coding.
Look up formReturn in the ObjectPal help, they have a good example of how to open a form using wait and formReturn.
I hope I didn't make this to confusing, I'm rushing trying to get out of the office.
If you want to attempt this let me know if and where you get stuck and I'll try and walk you through it.
Perrin