Selective DNS override

[stunted]

I have a number of devices inside my network that use pool.ntp.org or some *.pool.ntp.org as time server & my pfsense box uses sg.pool.ntp.org & aisa.pool.ntp.org along with running an NTP server itself, what I'd like to do is inside the network have *.pool.ntp.org point @ my pfSense box so devices inside use the NTP server running there & when my laptops etc.. are on the road they'll use the pool, but the problem is DNS overrides apply to the pfSence router itself so they'd break it's ability to set it's own clock.

Any ideas on how to achieve this? The easiest way I can think would be to change the NTP server my pfSense box uses but I face a similar problem with my apt proxy.