Yep. You can do this. No need for a second subscriber, just use an extra call-handler. That way you don't eat an Exchange box/licence.
In the CH that you use to dial the digits of the cell phone, make sure to use the Alternate transfer rule (it's the one that's enabled by default), or disable that rule and use another one. This trips a lot of people up since the Alt rule is set to not transfer. It's actually easiest to just set the Alt rule to transfer and use the Alt rule.