Parallel Universes aside, would be a miracle of theoretical physics
to have the mechanical brifter
and the hydraulic master cylinder occupying the same, limited space .. BUT..

TRP now sells a cable to hydraulic kit so you can use your Mechanical Brifters,
which brake by pulling a cable.
they include the slave cylinder for both wheels hose and a dual master cylinder
that fits under your stem.

or...
I hope you Got the road BB7, if you got the Mountain caliper ,
that is your problem .. wrong part bought.

even with the road caliper, you could use the inline travel agent..
that bolts onto your cantilever boss. with housing on both ends.
and you can set up the amount of travel increase ..

then get the adapter to install a 210mm disc, rather than a 160mm ..