which FM version ?
Sorry I forgot the mention
I use FM 9
On 9 you'll need an Event Script plugin that will fire upon exit the field ( on record commit )
Another option, that may or may not be useful is to run the script first and then pause for input.
Your script might look like:
Go To Layout [Search Layout (YourTable)]
Set Field [Yourtable::yourField; YourTable::YourGlobalField]
Set Error capture [on]
Perform Find 
#and so forth.
Now pressing the enter key will resume the paused script for you and perform the find.