Dear Sir,
unfortunately there is no such feature built into the product; but there are workarounds.

(BTW, I am sure you realize that if the OPC server indeed behaves as described, it is a bug in the server that should be primarily handled in there).

You can try to subscribe first with just one item, wait for some time, and then proceed with your other (many( subscriptions. The first item does not even have to be a valid one; in fact, choosing an invalid one (e.g. unknown Item ID) would probably be better, because it should be rejected right away and won't consume anything on the server side later.

It is also possible to achieve a similar effect by a dummy one-time operation, such as Read or Browse. In this case, however, care should be taken so that the wait delay is shorter than the (configurable) Hold period of the client, otherwise the connection might be closed before the "real" subscription occurs (which would then cause a re-connection, defeating the purpose).

Best regards