I'd assume it'd be a direction penalty on the IB skater - skaters can initiate blocks with straddling players, but those initiated blocks are subject to the normal standards.
If the block is legal (not stopped, not clockwise, etc.), then the straddling player just needs to figure out how to deal with it like any other skater a legal block is initiated on.
The straddling skater is technically considered out of bounds, so I don't believe they have position to lose.