[BSousa]

I think there are two options that play in your favour:

a) be honest, but when they ask (and they will) why you are leaving the current company, say you know they are paying their employees way below market rate. This allows you to tell the truth, but points out to the recruiter you will not take you current salary + 5%

b) redirect the question to "While I make X, I'm discussing the move with other companies and have offers for X+Y". This accomplishes two things, puts a premium on you (other companies are already interested you) and lets the recruiter know how much they will have to offer you to accept their offer.

Of course, you need to be ready for the conversation to fall through at this point, but you should always be ready for that anyway ;)