I'd give him Projection Modules, after all warlocks use those, don't they? I used for him my Warcaster specialist class, which allows him to Control constructs (which is very Solomon-related) and granting him a bit more HP and a nice discount on the Arcana Sephira Branch with Double Damage (Bellum Domini Archanum in Spanish...well Latin, actually...I don't know how it's called in English).
Also, my Matthew Gaul sheet has a unique Blood Legacy, Blood of Dominion, which is an enhanced version of Ancient Blood.
BLOOD OF DOMINION:
The character is a descendant of Andromalius.
Andromalius’ Power: The character has the Zen Ability and a bonus of +10 to the Base Presence.
Most Ancient Blood: The character is considered as benefitting from Ancient Blood, besides the character can connect to machines that only responded to Andromalius and his/her orders have for all original Lost Logia priority over those of any other one with Ancient Blood.
Natural Protocols: The character halves the MK cost of all Solomon’s Legacy Techniques and the DP and MK cost of Enhancing Protocol PT-01: Power-Up Magnus. The character is considered as having an extra Ki Reserve of 15 points per Experience Level he/she can only use to empower the Solomon’s Legacy Techniques, and an extra point of Accumulation each Even Level on Agi, Dex, and Pow characteristics.
LIMITS: This Blood Bond only pertains to Matthew Gaul, applying a Level Modifier of +2.
My personal Matthew Gaul sheet is capable of using all Solomon Protocols from the Dominus Exxet along with the Enhancing Protocol PT-01: Power-Up Magnus...which you can find somewhere else in this forum.
Note that the power level of my campaigns is pretty high, so Gaul is also granted a few spectacular Artifacts like the Spear of Andromalius (after all, that spear he's holding really looks like an artifact) and his Lord of War Armor which is an Arbiter Armor making him immune to mind reading and influencing effects and stuff like that.