Q: What can we do to make the back of the tongue elevate for /k/ and /g/?

We can use the Tongue Retraction Response (TRR) as follows:

Tactile stimulation down the midline of the tongue from anterior to posterior causes the entire tongue to retract back and up toward the velum. The response occurs about half-way down the tongue, and is elicited after the Tongue Bowl Response (TBR) and before the Tongue Gag Response (TGR). I also have called the TRR the “Pre-gag Movement” since it occurs before the gag and can act to prevent the gag. Its physiological function is to prevent foreign objects from reaching the oropharynx and setting off the gag. Upon visual inspection, the tongue appears like a ball or wad tucked up nicely in the oropharynx.

The TRR causes the whole tongue to lift, retract and make contact with the velum en masse. This position then can be held while the client exhales. Upon exhalation, a gross [+Back] phoneme will be elicited. Sometimes this will sound like a velar fricative (either voiced or voiceless) and other times it will sound like a gross [k] or [g]. The stimulation of the TRR therefore can be used to elicit a gross version of the refined positions necessary for all of the [+Back] raspberries, stops and fricatives.

The TRR will work in this manner only if the client has adequate oral-tactile sensitivity. If sensitivity is low (hypo-sensitivity), the client may not respond at all. If sensitivity is too high (hypersensitivity) the stimulation will set off the gag. Therapy then must account for these sensitivity differences. Techniques are employed to normalize sensitivity prior to or simultaneously with the TRR.

More techniques for /k/ and /g/ can be found in my post, Stimulation Techniques for K and G.