You cannot make a multi-user file in run-time. Also I read that you can if you place it on FM server. But I guess you still need client FMPs.
The reason is that you would need several other interfaces to read it and in the run-time these are bound (there's no development environment to use as application reader. This is so also so that FM inc. makes more money. FMP is a terrific product (because it's so easy) not because it's inexpensive. As soon as you start having some people on an intranet using it becomes costly compared to some other very powerfull but hard to master alternatives. The lesson is you pay extra in order to be able to put toghether something quite complex without a lot of knowledge. So the deal is quite ok.