I think it was just a decision on the part of the band to honour hide by leaving his solos exclusively his.
Then again, "his" solos are completely random.
So far, these are the songs where Sugizo plays the solos with Pata:
Silent Jealousy (first song ever to do and now on every concert; an exception was hide memorial summit)
I.V. (on every concert)
Orgasm (on every concert, if it's played)
X (on every concert)
Blue Blood (at countdown gig, only one so far)
Jade (on every concert)
Born to be free (on every concert)
Endless Rain (started recently at the tour)
hide gets the rest, like Rusty Nail, Week End, Kurenai, Drain, Art of Life, Dahlia...
So the question here is, what's the parameters to consider them "his" (hide's) solos? Wasn't I.V. very specifically made with hide's solo? Then why Sugizo plays it? Aren't Silent Jealousy and Endless Rain is work too? Again, it's all completely random. There's no fixed pattern to tell which solos "belong" to hide.
Most importantly, and I say it without resentment, hide is dead and he has no action or vote on what X JAPAN does now. The songs hide appears in are completely based on what others decide to do, he has nothing to do with this show and is merely an object. Of course I won't discuss that his spirit is present, he's beating inside the soul of X, he lives through what he wrote, through what he did, but he's doing nothing now. Others are manipulating what "hide" is now.
In resume, I don't think there's a specific reason or pattern why Sugizo should play these or these solos. I think the band sounds more powerful when it actually plays 100% live. It's hard to do real good rock using pre-recorded guitars.
My two cents.