This article explains the method for using VISA to write an interrupt out pipe to a USB RAW device from LabVIEW.
You can accomplish this transfer by setting a USB VISA property node to USB Settings » Out Pipe (also called "Bulk Out Pipe" before NI-VISA 3.5) and then doing a VISA Write as illustrated in the image below.
It is important to remember to properly set the class of the VISA resource to USB RAW by right-clicking the VISA resource name and selecting Select VISA Class » I/O Session » USB RAW. If the VISA class is improperly set, you will not get the correct options in the property node. The VI shown in the snippet above is also attached below for use in LabVIEW 2011 or later.