Hamilton's investment, £1.6m of equity over a 10-year period, was enhanced by hands-on involvement with the group as it built a blue-chip customer base in the then unfashionable area of corporate expense management.
"The MPs' expenses scandal helped," Mr Boyle said. "Instead of expenses being a housekeeping matter, it became a moral compass of how you run your company. People realised it can be very damaging and they had to take it a bit more seriously."
Global Expense clients include British Airways, Sainsbury's, Fujitsu and Asda. It is headquartered in London with a processing centre in Kent.
Mr Boyle said: "This is a successful example of venture – not vulture – capitalism."
Hamilton has been deeply involved in the management and operation of Global Expense for 10 years and the staff, who owned 10% of the firm, were delighted to receive £1.4 million.
"Following the acquisition there were no redundancies and staff numbers at Global Expense have actually increased," said Mr Boyle. "Concur has also relocated some of its European-based personnel and processing to Kent – a genuine testimony to the company's success. It has been a real win-win-win – for the staff, investors and a great strategic buy for Concur."
It is Hamilton Portfolio's most notable deal since it sold luxury travel group CV Travel to Kuoni in 2007, three years after buying it.
"We turned that around, bought it for £5m and sold it for £16m, so that was rather good," Mr Boyle said.
When buying into Global Expense it had been "very much an unpolished idea", he said, but "at the end what happened was we got a couple of very significant pieces of business."
Mr Boyle set up Hamilton Portfolio in 2002 after he and brother Hugh sold their own start-up Direct Holidays to Airtours for £84m.
They also founded airline Zoom, which fell victim to the credit crunch in 2008.
Mr Boyle said the portfolio had more than £20m in property holdings and about £10m in non-property investments.