I agree with Easy peasy.
The transfer function changes between DCM and CCM, so it is much more difficult to make the regulator loop if both modes are allowed.
I think it could be possible with a fully digital regulator that can detect the change between DCM and CCM, and quickly change the regulator equations.
Remember that we want minimal distortion in the current, so a "normal" regulator is probably not good enough.
To be in DCM, the Vs (Volt*second) when taking energy from the inductor must be higher than the Vs when putting energy into it.
D = switch on, so Vin is applied to the inductor
The rest of the time is (1-D), where Vout is applied to the inductor until the current reaches zero.
This means that Vout * (1-D) must be greater than Vin * D if the mode must be DCM.
Vout * (1-D) > Vin * D
Divide by (1-D) on both sides:
Vout > Vin * D / (1-D)