The institute would provide help and advice for voluntary sector managers.
"The most selfless individuals who work 16 hours a day running voluntary groups, campaigns or charities come across as beleaguered, exhausted and overwhelmed," Clegg told Third Sector after delivering a speech to charity chief executives at the NCVO this week.
According to Treasury estimates, charities fail to claim Gift Aid worth £700m each year.
Clegg also said there ought to be an independent inquiry into whether Criminal Records Bureau checks were discouraging potential volunteers.
He questioned whether the checks ought to dredge up minor offences on police files: "Pressure needs to be put on the way checks are conducted and on the way data is retained and exposed by those checks."
Charities were about "passion, not paperwork", he said.