Set Inventory organization selection for custom form

Call procedure FND_ORG.CHOOSE_ORG in PRE-FORM to ensure the organization parameters are set.

You need to define 3 parameters in your FMB to make procedure work.
ORG_NAME
ORG_CODE
CHART_OF_ACCOUNTS_ID

Other useful FNDSQF Routine API's
http://docs.oracle.com/cd/E18727_01/doc.121/e12897/T302934T462356.htm