Noticed no replies to this issue. A related, brief post is here:
http://support.empirisoft.com/showthread.php?t=8115
The post above addresses a core issue to the pip and pop paradigm, namely trials with a single stimulus, followed by trials that pair a second stimulus with the first.
If you have not already, you might review the samples in your DriectRT folder: ...\DirectRT\Samples\5 - other features
Some of these samples would give you a framework to adapt to your research design.
If you'd like, I'm glad to assist you further.