Checking For Field Value in Customer Group From Invoice Entry

I am trying to come up with a custom solution, and I’m hoping someone here can guide me in the right direction.

In AR Invoice Entry, I have created a custom epiButton on the Header tab.  When an invoice is displayed in the window, I would like to check the value in a checkbox01 custom field in the Customer Group table, for the customer that is assigned as the sold to on the invoice.  I would then like to enable/disable the epiButton based on if the checkbox field value is True or False.

I have so far created a BPM that fires on the Erp.ARInvoice.GetByID event.  At this point I’m not sure where/how to add custom code that would go to the CustGroup table and grab the checkbox01 value, and then set the Enabled properties of the epiButton.

I also have the Epicor Customization Tools add-in extension for Visual Studio.  Would it be better to program the logic in that rather than the BPM?  If so, how can I add in any references to the CustGroup table, or run a BAQ looking at CustGroup?

Any advice/guidance would be helpful.

Thanks in advance.