It sounds like you have connected your Pi to your mobile phone to give it internet access. Ad-Hoc is a one-to-one network connection, so the topology looks like this.
So an easy way is to get a Wireless range extender. If you are within the same building, but don't have access to the main router for some reason? This makes sense, but the max speed is not true max speed any more, it will be less than connected to the main router.
But if you can run a cable from the router, or from your extender (usually they have a 4 LAN ports) but you can also use PowerLine LAN, this will give you pretty good results on speed. Then make your Pi work like an access point for other devices to connect. The advantage is that everybody and every device is on the same network now, and you can airplay from wherever you are connected, even remote Wifi, with a LAN backbone to the main router.
There is a fantastic write up in MagPi magazine, Issue 11, on how to set up your Pi as a Pi-Point as they coined it. But you may want to skip setting up DHCP server or DNS, since you want your main router to keep all devices registered and happy in one place, so that everybody can talk to each other. DNS on the Pi will be the IP of the main router, since the main router can tell you who is on your network, or lookup internet domains. It works pretty good.
And purposely I left the answer to your question last, because it is the most complicated and awkward way to setup a network. It may seem like the right thing to do, but you should realise, ad-hoc, in it self mean peer-to-peer. So thats it, you cant connect more in between there. What you can do, though, and this is the complicated and awkward part, is to bridge your adhoc network with your main network. But, you said you cant connect yo your main network, so you have to do one of the steps above before you can bridge with anything. But that will solve the whole problem of network issues anyway.
Essentially, the answer to your question, as it stands, is No.