You could use an high voltage probe expressly designed for extending the DMM voltage range, as the following from Fluke:
Description excerpt (emphasis mine):
The 80K-40 is a high voltage probe designed to extend the voltage measuring capability of an AC/DC voltmeter to 40,000 volts peak AC or DC Overvoltage Category I. This means the probe can only be used to make measurements on energy limited circuits within equipment. Examples include high voltage within televisions or photo copy machines. DO NOT use this probe to measure high voltages on power distribution systems. The probe provides high accuracy when used with a voltmeter having 10 Megohm input impedance.
Note that cat II, cat III, etc., rating has more to do with the energy capability of a system than with its voltage level. I.e., cat II rating should be more than enough to protect you from accidental faults when doing measurements inside a scope, provided you use a meter+probe set that can withstand the voltages inside.
Of course, I'm assuming you are using a floating, i.e. non mains-powered, instrument.
EDIT (to answer a comment about cat ratings)
See this document from fluke about cat ratings. Excerpts (emphasis mine):
The real issue for multimeter circuit protection is not just the maximum steady state voltage range, but a combination of both steady state and transient overvoltage withstand capability. Transient protection is vital. When transients ride on high-energy circuits, they tend to be more dangerous because these circuits can deliver large currents. If a transient causes an arc-over, the high current can sustain the arc, producing a plasma breakdown or explosion, which occurs when the surrounding air becomes ionized and conductive. The result is an arc blast, a disastrous event which causes more electrical injuries every year than the better known hazard of electric shock.
And also this one:
It’s not just the voltage level
In Figure 1, a technician working on office equipment in a CAT I location could actually encounter dc voltages much higher than the power line ac voltages measured by the motor electrician in the CAT III location. Yet transients in CAT I electronic circuitry, whatever the voltage, are clearly a lesser threat, because the energy available to an arc is quite limited. This does not mean that there is no electrical hazard present in CAT I or CAT II equipment. The primary hazard is electric shock, not transients and arc blast. Shocks, which will be discussed later, can be every bit as lethal as arc blast.