Communicate s7-300 via profibus

Hello there folks!

I need to access certain DB data from slaves (IM 151, CP342-5) connected to master (CPU 315-2 PN/DP) via Profibus-DP. They're all connected to a supervisory system, which can access data from all modules.
The problem is i'm allowed to program the master only. I came up with 3 possible solutions: Global Data (GDC), routing and PUT/GET (IM 151 not capable of S7 connection).
Considering that GDC requires that every module has the latest hardware configuration (which i can't download to slaves), is routing the only solution? If so, how to access data from an OPC server connected to master?

Post Scriptum: Sorry for broken english. Please, if i omitted any information that may help, feel free to ask. I intend to answer ASAP

Actually the remote I/O IM151 used is capable of S7 connection. Therefore, PUT/GET were used.

Yes, you should be able to use PUT/GET. Since you aren not allowed to make changes in the slaves, it seems to be the only way to do it.
I assume that the "IM151" is an IM151-7. In this one you have to activate the "test, commisioning, routing" in the setup of the DP port.