This workflow is practically guaranteed to fail.
You certainly could create the whole thing as a series of illustrator files that can be placed, but how is the client going to edit them? If he has ID CS1, his Illustrator is likely just as out of date and will have problems with your newer files, most likely converting all of the text to "point text" rendering it pretty useless.
This type of question comes up quite often although generally, we are not discussing a gap of six full CS releases (CS5.5 was really a full release, especially of InDesign) covering a period of over eight years.
Although you could probably cobble up some really Byzantine kludges to round-trip content between CS1 and CS6 InDesign versions, you should consider two other things:
(1) It is highly likely that no matter how careful you are, you are going to encounter anomalies going back and forth that will either take significant amounts of your time to work around or in the even worse case, you don't even find until very late in the workflow or on the press. And your level of frustration may be stratospheric!
(2) Your time and that of your client is worth something. Unfortunately, most professionals in the graphic arts industry vastly undervalue their time as opposed to obsessing on the cost of keeping their tools (in this case, software) fairly up-to-date and in sync with those they work with. My bet is that the cost of software upgrade by your client will be vastly overshadowed by value of time wasted by him hacking around to get this workflow viable plus the higher costs you pass on to him based on the extra time you are expending due to his failure to upgrade. If you are not charging extra for this, you should be.
If you want to be of value to the client point them to Creative Cloud. There is no way in hell you will get that workflow to work.
Thanks Dov [and all the others who have commented],
I think I just want to be sure that theres no stone unturned if I make a recommendation to the client that he upgrades to Cloud or Design Standard CS6. The issue is slightly greater in that it also probably involves a hardware upgrade [totally new PC with Windows 7 which may then have issues with his works network configuration] so its quite the outlay for the client with some risks involved.
Anyway, I really value the feedback on this.