In one trunk out another - a better way?

I want calls coming in one trunk (zap) out another trunk (sip) transparently to the caller. One way that comes to mind is to modify the inbound route for zap and connect the 'set destination' to a custom destination as follows:

[cust-fwd]
exten => _X.,1,Answer()
exten => _X.,n,Dial(SIP/${EXTEN}@siptrunk.com)

Is there a simpler way to do this? (bridge trunks directly?)