So, if I understand this correctly what you are looking for is when on a call on a Call key, another call (or third call, etc) is presented to the phone and you are just pressing the next Call key and the first call is dropping and you want it to automatically be placed on hold instead of pressing the Hold button then the ringing Call key? Is that the correct scenario? If so, this there is no option in the 5000 for this, you need to press the Hold button to place the first/second call on hold.
All features of the 5000, either set based or system wide, are handled via Flags... For system-wide flags see System->Flags and for phone level look at System->Phone-Related Information->Flags (opening each one will give you a list of phones that have that flag enabled, you can add/remove from here) or open a phone and then flags to see what flags are enabled/disabled on that specific set.