Putting index entries to XLog

Hi *,
I have encountered a problem while implementing an index structure. I don't have any access to the RM (I don't know, how to set it up properly) using my index. However, when I don't have the situation of working with a temporary table, I need to put entries using XLogInsert(...). The problem for me is, that based on the fact, that I don't have the access to the RM, I can't put proper entries to the xlog facility. How can I achieve that my index structure can be stored properly at least?
I'm getting lots of errors, when I just put a XLogRecPtr with data {1,1} as LSN of the page. On the other hand when doing XLogInsert calls to work with the component properly I don't know which data to put in there. When I'm using some kind of RM_ID (like RM_GIST_ID or something like that) I'm getting problems because I don't know which code to insert there. I decided to take RM_GIST_ID and an invalid code (so it won't call any of the xlog gist implementations upon recovery) which, however failed, too. Unfortunately my task is to implement a certain structure with PostgreSQL, so all of my current work actually depend on this action.
I hope that somebody will be able to help me according to this issue.
Thanks in advance

Best regards
Carsten Kropf