opposite of relativistic time contraction

Suppose we have an intelligent species with control over godlike amounts
of matter and energy. They can make black holes from scratch, for
instance. Now let's say they want to make time flow more rapidly
for a certain observer than for the observers out in flattish spacetime.
For instance, maybe this observer wants to be able to play chess, and
have 10x more time to think about his moves than he otherwise
would have. Is this possible? The reverse effect is, of course, fairly
trivial: either spend some time traveling at relativistic speeds, or
go down into the gravity well of a black hole (I guess one sufficiently
massive so that its tides don't hurt you). But if you want to have
*more* time pass for you, the only possibility I can think of is that
maybe you could obtain some negative mass (assuming that such a thing is
allowed by the laws of physics, and you know where to get some), and
make a negative-mass black hole out of it; IIRC the time dilation effect
is phi/c^2, where phi is the gravitational potential, so for phi>0 you'd
get the desired effect.

Are there thermodynamic issues? Is such a technology equivalent to
the ability to make spacetimes with closed timelike curves?

A somewhat related question is what is the simplest/cheapest/least
disruptive way for such a godlike species to apply large accelerations
to observers for a long time without ripping them apart with tidal
forces. It's easy to apply a large acceleration for a short time:
just move a microscopic black hole close to him, and you can easily
obtain accelerations of, say, 1000 m/s2 with negligible tidal effects,
without getting him anywhere near its microscopic event horizon.
But to apply such an acceleration for a long time (as would be
necessary, e.g., if you want to accelerate him up to relativistic
speeds), you need to be able to apply an acceleration to the black
hole as well. For that purpose, I guess you have to charge up the
black hole, and my first attempts at back-of-the-envelope calculations
seem to show that the result would be that the area around the black
hole would have to have gigantic electric fields, incompatible
with the existence of matter. Assuming you can solve that problem,
it would seem to be easier to bend your astronaut's trajectory
than to speed him up or slow him down, since a change in speed
requires either an input of energy (which could be expensive) or
the dissipation of energy (which is difficult to do thermodynamically).
I'm vaguely visualizing something like a train or conveyer belt
made out of charged microscopic black holes strung together...?