Related Information Section - Making it required

We are using custom object 5 called Initiatives. We are creating a web applet to to allow the user to create multiple initiatives tied to an opportunity. There could be multiple initiatives tied to an opportunity and the user would need to add the percentage for each initiative and initiative detail. Also there are some rules and validations that need to occur when adding the initiative records.Hence we are planning to create a web applet with custom development. The web applert would be added as a related information section within the opportunity.

Question: How do we force the user to add these initiatives for certain opportunity types within the related information and not allow the user to advance the opportunity to next stage unless the intiatives have been added to the opportunity. It looks like OnDemand does not have the ability to force the user to add information section for Opportunities,Accounts.