I have the copy of the CAFE test of Cozy Mk IV canard where it states
that swept wings tend to start stalling at the tip rather than the root.
This moves the center of lift forward and is a bigger problem for aft
CG.

By the very nature of a canard configuration, if the aft wing stalls,
the tip will stall first, as it it in the upwash caused by the tip
vortex coming off the canard. The inboard part of the aft wing is in
downwash from the canard. With that said, the aft wing of a canard
aircraft should NEVER be allowed to stall. If it does, the neutral
point will shift forward and the aircraft will become longitudinally
unstable. The idea is for the canard to stall first. This makes the
airplane more stable and causes the nose to pitch down.

While canard planes swept wings typically already have those
"vortilon" tabs, has anyone investigated placing a few vortilons near
outer wing part to compensate for the early tip stall tendency?

The vortilons are always placed on the outer part of the aft wing of a
canard configured aircraft, to keep the outer aft wing from stalling.
There is no sense on placing them on the inboard wing, unless the
aircraft is really screwed up.

On early VariEzes, it was found that the outboard portion of the aft
wing, of poorly built aircraft, would stall. Rutan retrofitted a cuff
on the outboard aft wing, to prevent this stalling.