Drag and Drop Field evaluation in a portal

Dear Forum,

I am building a quoting database using the separation model.

I am dragging a number (a value) from one window to another window, right into the last row of a portal into a field

that is the field that needs this number.

However, I only want to permit this drag and drop of the number into that field IF this portal for fills certain conditions.

I can easily limit the drag and drop with the FM 11 script triggers IF i am in the portal field (the on object enter).

However when dragging I never enter the object (since I drag- obviously).

I tried to set the field options to check for the certain condition and to use only the value if the certain condition is met- but to no avail.

How can I somehow track that record that I am committing upon dropping, possibly delete it right after entering?

Thank you!