If you like that...:
I find that its hard to keep a skilled glassmaker busy while NOT wasting his time gathering sand (which is unaffected by skill)
So I build several glassmaker's furnaces (either magma or regular, but usually regular so they can be near the sand) Then I designate an army of dwarves to gather sand. Set the shops up with 1 order to gather sand on repeat, and 9 orders on suspension.
Then I build 1 shop for THE glassmaker (restrict who can use it with P), and just use the manager to queue up glass jobs. Since the other shops are full of useless orders, the manager fills only the 1 shop with orders for the skilled glasser. And there is always spare sand... assuming I can spare the laborers.
It's fairly self managing, but not fool proof.
The above solution won't work well if you want to use both workshops at the same time.
I would suggest using stockpile/workshop links (take from, give to). There would be a lot of cancellation spam, but eventually, the jobs would get done at the right workshops. Actually, this method is still kind of bad.
This is true.
Though I wouldn't say "it won't work" -- it will just be a little clumsy. You can still use the other shop as long as it is always full. jobs either need to be suspended or on repeat with no chance of cancellation (use Dfhack's workflow manager?).