How to force a refresh on a custom transaction column via script?

I have a process during sales order entry where I have a need to refresh the drop-down values of a custom sourced field on my order line, but cannot find a way to do this.  I am using nlapiSelectNewLineItem to create a new order line, nlapiSetCurrentLineItemValue to set some values on the line, and finally using nlapiCommitLineItem to commit the line to the order. 

While I am setting values on the line, I also am creating some supplemental records, and this is where my sourced field comes into play.  My sourced field is based on the custom records I am creating while I am populating the order line values.  When it comes time for me to set the value of the sourced field, the value I need is not available because the drop-down values need refreshed to acknlowedge the custom records I just created.