Conditional Validation on a BlockType/PageType

I have a Block Type wich has these two properties.

[CultureSpecific]
[Display(
Name = "Display PDF Button", GroupName = TabNames.PDFCustomisation, Order = 0)]
public virtual bool DisplayPdfButton { get; set; }
[CultureSpecific]
[Required]
[Display(
Name = "Download Pdf Text", GroupName = TabNames.PDFCustomisation, Order = 1)]
public virtual string DownloadPdfText { get; set; }

I only want DownloadPdfText to be required if the user sets DisplayPdfButton to True. - Is this possible to do in Episerver?