There's no point. That connection won't save enough (over departing from Kingston itself) to make it worthwhile. It's an hour to drive from Kingston to Sharbot Lake. With travel times from there, it would be a wash compared to what is there today. Also, if Kingston passengers get diverted to HxR, the business case for Lakeshore services as a whole gets seriously damaged.
Right now, travel times are;
Kingston-Toronto: 2.5 hrs
Kingston-Ottawa: 2.3 hrs
Kingston-Montreal: 2.75 hrs
Making the Kingston trains all stop milk runs might add 10-15 mins more (they already have some stops), but those are still relatively decent travel times. What's needed is better air-rail integration including the REM Extension at Dorval and extending Lakeshore service thru Union to terminate at Pearson. Being able to get to Dorval or Pearson in less than 3 hrs from Kingston or to Ottawa in closer to 2 hrs would be massively beneficial. Not just to Kingston. But for the entire Lakeshore.