At this point, there's no real reason to trade for UFA rights as of now. You can talk to the UFAs - including general parameters.
So saying to them 'Hey, if we get Spezza we would be interested in you as well.' and then giving the general idea of term and money you'd give them is perfectly acceptable. Just nothing is binding at that point. So I mean, I suppose if you can get the deal done - you might want the rights just to ink those deals too - but at best you're getting like a 7th round pick probably.