Default Date to 1st of the year [01/01/year]

Hello,

I would like to default a 'DateField' to the 1st of January for the year when a record was created. Examples are shown below

DateField           Default to

[12/05/2014]     [01/01/2014]
[13/09/2010]     [01/01/2010]
[24/10/2013]     [01/01/2013]

I thought of having a Workflow that would be triggered when the record is created and then call a J-Script that would default the date to the 1st of the Year (i am not sure if its possible to call J-Scripts from WorkFlows).

Any ideas and advice would be appreciated because i don't know how achieve this ?

Many Thanks