Bootstrapping in discontinuous mode
If you need a galvanically isolated control, then why not to use opto coupled gate driver instead of making separate opto coupler + gate driver.
In this example you have a device that does the job for you. The gate power supply Vcc can be a galvanically separated DC/DC converter from your's 5V to 15V.
This is how it looks like (https://www.eeweb.com/blog/avago_technologies/isolated-igbt-mosfet-gate-driver-evaluation-board):

You can see, that unpopulated holes are the place for standard DC/DC converter.
Having a constant gate power supply you can make a duty cylcle from 0% to 100% without problems, which is an unresolvable task for bootstrapping technique, IMO.