Thank you for your question. I look forward to working with you to provide you the information you are seeking.
I am afraid that even charging them for items indirectly could violate the terms that you have posted above. These companies are very vigilant at protecting their property, so they will likely sue you if you are seeking to infringe on their rights as outlined in their terms. Unfortunately, the legalities often hit people at the end instead of the beginning because they do not think of the legal issues when they are working on an idea. Without negotiating some deal with this company to perhaps share some proceeds with them in exchange for a license agreement to do this, I am really afraid that you could be sued here if you directly or even indirectly sell people items that could allow them to buy items in the game itself and that is the key, even though the credits are proprietary to your idea.
I truly aim to please you as a customer, but please keep in mind that I do not know what you already know or don't know, or with what you need help, unless you tell me. Please consider that I am answering the question or question that is posed in your posting based upon my reading of your post and sometimes misunderstandings can occur. If I did not answer the question you thought you were asking, please respond with the specific question you wanted answered.
Kindly remember the ONLY WAY experts receive any credit at all for spending time with customers is if you click on OK, GOOD or EXCELLENT SERVICE even though you have made a deposit or are a subscription customer. YOU MUST COMPLETE THE RATING FOR THE EXPERT TO RECEIVE ANY CREDIT, if not the site keeps your money on deposit.
Also remember, sometimes the law does not support what we want it to support, but that is not the fault of the person answering the question, so please be courteous.
This is NOT the practice of law nor is it legal advice to you, it is merely educational information for you to use to seek out a licensed attorney in your state to get actual legal advice from them. Please use sites such as http://www.martindale.com or http://www.lexmundi.com or http://www.hg.org to find a local attorney to get actual legal advice in all matters.