Not an easy one to answer with no remote control or local admin. Depending on the global region, Christmas day could be an option with a larger upgrade window (downtime) for the ISO image over the WAN. Other that that you are going to really struggle with those 128k links and no local servers to host the ISO by postal USB.
I would be interested to know your reason for the upgrades and also what the sensor-ve is typically giving you above and beyond the Netflow export available from the remote Steelhead.
I would also be interested to know your plans with your sensor-ve estate as they are end of feature software release December 2014.
If i understand right - there's no way to partially upload update.
Reasons are: in initial configuration we locally upload Sensor-VE package version 10.0.1
After installation some devices we find, that they can't connect to profiler, one of advice was to upgrade Sensor-VE to 10.0.7 version. And the next my investigation was - how we can do this task on all devices, without local update.
Some of devices can be updated simply, they have good network channel.
But some with very bad channel located in difficult to access locations.
ok we'll plan to local update, but the best solution which is interest is partally upload to a steelhead/sensor-ve, not local PC.
I can ask my colleague about number of ticket, where he discuss this problem
About our plans on this devices, i think we should continue in email, not this thread