You have a keywords field on a form and want the list of values to be dynamically filled up and not just a simple lookup into a view. The trick here is to look into the documents already created for the values of the keywords.
First make a note of all the keywords fields that you want a dynamic lookup.
Create a hidden view which displays the documents created through the form in question.
Add a column for each of the keywords fields that you have listed. Make sure you sort the column in the order you want.
Now make a @DbColumn to the appropriate column in this view for the appropriate keyword field. You may want to use @Unique if you want unique values in the keywords list.
This is useful if the keywords field property 'Allow values not in list' is selected. This would make the values in the list grow dynamically as more new keywords are added.